filter: Add dropped_bytes_total / drop_bytes metrics

[cosmo0920]

To observe more precisely for filter plugins, we need to add dropped bytes metrics into ordinary metrics for filter plugins.
The dropped size should be a monotonic value. So, I choose counter type of cmetrics to handle it.

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Enter [N/A] in the box, if an item is not applicable to your change.

Testing
Before we can approve your change; please submit the following in a comment:

• Example configuration file for the change

[SERVICE]
    HTTP_Server On
    HTTP_Port 2020

[INPUT]
    Name dummy
    Dummy {"endpoint":"localhost", "value":"something"}
    Tag dummy

[FILTER]
    Name grep
    Match *
    Exclude value something

[OUTPUT]
    Name stdout

• Debug log output from testing the change

% bin/fluent-bit -c grep.conf -v
Fluent Bit v3.2.0
* Copyright (C) 2015-2024 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

______ _                  _    ______ _ _           _____  __  
|  ___| |                | |   | ___ (_) |         |____ |/  | 
| |_  | |_   _  ___ _ __ | |_  | |_/ /_| |_  __   __   / /`| | 
|  _| | | | | |/ _ \ '_ \| __| | ___ \ | __| \ \ / /   \ \ | | 
| |   | | |_| |  __/ | | | |_  | |_/ / | |_   \ V /.___/ /_| |_
\_|   |_|\__,_|\___|_| |_|\__| \____/|_|\__|   \_/ \____(_)___/

[2024/09/25 13:23:44] [ info] Configuration:
[2024/09/25 13:23:44] [ info]  flush time     | 1.000000 seconds
[2024/09/25 13:23:44] [ info]  grace          | 5 seconds
[2024/09/25 13:23:44] [ info]  daemon         | 0
[2024/09/25 13:23:44] [ info] ___________
[2024/09/25 13:23:44] [ info]  inputs:
[2024/09/25 13:23:44] [ info]      dummy
[2024/09/25 13:23:44] [ info] ___________
[2024/09/25 13:23:44] [ info]  filters:
[2024/09/25 13:23:44] [ info]      grep.0
[2024/09/25 13:23:44] [ info] ___________
[2024/09/25 13:23:44] [ info]  outputs:
[2024/09/25 13:23:44] [ info]      stdout.0
[2024/09/25 13:23:44] [ info] ___________
[2024/09/25 13:23:44] [ info]  collectors:
[2024/09/25 13:23:44] [ info] [fluent bit] version=3.2.0, commit=41b90b777c, pid=647
[2024/09/25 13:23:44] [debug] [engine] coroutine stack size: 36864 bytes (36.0K)
[2024/09/25 13:23:44] [ info] [storage] ver=1.5.2, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2024/09/25 13:23:44] [ info] [cmetrics] version=0.9.6
[2024/09/25 13:23:44] [ info] [ctraces ] version=0.5.5
[2024/09/25 13:23:44] [ info] [input:dummy:dummy.0] initializing
[2024/09/25 13:23:44] [ info] [input:dummy:dummy.0] storage_strategy='memory' (memory only)
[2024/09/25 13:23:44] [debug] [dummy:dummy.0] created event channels: read=21 write=22
[2024/09/25 13:23:44] [debug] [stdout:stdout.0] created event channels: read=23 write=24
[2024/09/25 13:23:44] [ info] [output:stdout:stdout.0] worker #0 started
[2024/09/25 13:23:44] [ info] [http_server] listen iface=0.0.0.0 tcp_port=2020
[2024/09/25 13:23:44] [ info] [sp] stream processor started
^C[2024/09/25 13:23:52] [engine] caught signal (SIGINT)
[2024/09/25 13:23:52] [ info] [input] pausing dummy.0
[2024/09/25 13:23:52] [ info] [output:stdout:stdout.0] thread worker #0 stopping...
[2024/09/25 13:23:52] [ info] [output:stdout:stdout.0] thread worker #0 stopped

$ curl localhost:2020/api/v1/metrics
{"input":{"dummy.0":{"records":0,"bytes":0}},"filter":{"grep.0":{"drop_records":4,"add_records":0,"records":4,"bytes":0,"drop_bytes":228}},"output":{"stdout.0":{"proc_records":0,"proc_bytes":0,"errors":0,"retries":0,"retries_failed":0,"dropped_records":0,"retried_records":0}}}

curl localhost:2020/api/v2/metrics                                                                               [OK]
2024-09-25T04:24:15.750972436Z fluentbit_uptime{hostname="Hiroshis-MacBook-Pro.local"} = 7
2024-09-25T04:24:08.747121548Z fluentbit_input_bytes_total{name="dummy.0"} = 0
2024-09-25T04:24:08.747121548Z fluentbit_input_records_total{name="dummy.0"} = 0
2024-09-25T04:24:14.751790810Z fluentbit_filter_records_total{name="grep.0"} = 6
2024-09-25T04:24:14.751790810Z fluentbit_filter_bytes_total{name="grep.0"} = 0
2024-09-25T04:24:08.747220046Z fluentbit_filter_add_records_total{name="grep.0"} = 0
2024-09-25T04:24:14.751790810Z fluentbit_filter_drop_records_total{name="grep.0"} = 6
2024-09-25T04:24:14.751790810Z fluentbit_filter_drop_bytes_total{name="grep.0"} = 342
2024-09-25T04:24:08.747280629Z fluentbit_output_proc_records_total{name="stdout.0"} = 0
2024-09-25T04:24:08.747280629Z fluentbit_output_proc_bytes_total{name="stdout.0"} = 0
2024-09-25T04:24:08.747280629Z fluentbit_output_errors_total{name="stdout.0"} = 0
2024-09-25T04:24:08.747280629Z fluentbit_output_retries_total{name="stdout.0"} = 0
2024-09-25T04:24:08.747280629Z fluentbit_output_retries_failed_total{name="stdout.0"} = 0
2024-09-25T04:24:08.747280629Z fluentbit_output_dropped_records_total{name="stdout.0"} = 0
2024-09-25T04:24:08.747280629Z fluentbit_output_retried_records_total{name="stdout.0"} = 0
2024-09-25T04:24:15.750972436Z fluentbit_process_start_time_seconds{hostname="Hiroshis-MacBook-Pro.local"} = 1727238248
2024-09-25T04:24:15.750972436Z fluentbit_build_info{hostname="Hiroshis-MacBook-Pro.local",version="3.2.0",os="macos"} = 1727238248
2024-09-25T04:24:15.750972436Z fluentbit_hot_reloaded_times{hostname="Hiroshis-MacBook-Pro.local"} = 0
2024-09-25T04:24:15.751103393Z fluentbit_storage_chunks = 0
2024-09-25T04:24:15.751103393Z fluentbit_storage_mem_chunks = 0
2024-09-25T04:24:15.751103393Z fluentbit_storage_fs_chunks = 0
2024-09-25T04:24:15.751103393Z fluentbit_storage_fs_chunks_up = 0
2024-09-25T04:24:15.751103393Z fluentbit_storage_fs_chunks_down = 0
2024-09-25T04:24:08.747121548Z fluentbit_input_ingestion_paused{name="dummy.0"} = 0
2024-09-25T04:24:13.750772332Z fluentbit_input_storage_overlimit{name="dummy.0"} = 0
2024-09-25T04:24:13.750772332Z fluentbit_input_storage_memory_bytes{name="dummy.0"} = 0
2024-09-25T04:24:13.750772332Z fluentbit_input_storage_chunks{name="dummy.0"} = 0
2024-09-25T04:24:13.750772332Z fluentbit_input_storage_chunks_up{name="dummy.0"} = 0
2024-09-25T04:24:13.750772332Z fluentbit_input_storage_chunks_down{name="dummy.0"} = 0
2024-09-25T04:24:13.750772332Z fluentbit_input_storage_chunks_busy{name="dummy.0"} = 0
2024-09-25T04:24:13.750772332Z fluentbit_input_storage_chunks_busy_bytes{name="dummy.0"} = 0
2024-09-25T04:24:08.747280629Z fluentbit_output_upstream_total_connections{name="stdout.0"} = 0
2024-09-25T04:24:08.747280629Z fluentbit_output_upstream_busy_connections{name="stdout.0"} = 0
2024-09-25T04:24:08.747280629Z fluentbit_output_chunk_available_capacity_percent{name="stdout.0"} = 100

• Attached Valgrind output that shows no leaks or memory corruption was found

==18599== 
==18599== HEAP SUMMARY:
==18599==     in use at exit: 0 bytes in 0 blocks
==18599==   total heap usage: 54,246 allocs, 54,246 frees, 14,867,130 bytes allocated
==18599== 
==18599== All heap blocks were freed -- no leaks are possible
==18599== 
==18599== For lists of detected and suppressed errors, rerun with: -s
==18599== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

If this is a change to packaging of containers or native binaries then please confirm it works for all targets.

• Run local packaging test showing all targets (including any new ones) build.
• Set ok-package-test label to test for all targets (requires maintainer to do).

Documentation

• Documentation required for this feature

Backporting

• Backport to latest stable release.

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.