Add format=badge which directly serves badges

[vaskozl]

Adds support for directly generating badges so as to remove the need for shields.io.

I've added DejaVuSans.ttf to the container as go-badge requires a font in order to calculate spacing. Another font can also be configured and mounted in the container if desired.

Example:
https://kromgo.sko.ai/query?metric=nodes&format=badge

[vaskozl]

Apache Bench on my machine:

vasko@anchor ~ % ab -n 100 -c 10 'https://kromgo.sko.ai/query?metric=pods&format=badge'
This is ApacheBench, Version 2.3 <$Revision: 1903618 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking kromgo.sko.ai (be patient).....done


Server Software:        
Server Hostname:        kromgo.sko.ai
Server Port:            443
SSL/TLS Protocol:       TLSv1.2,ECDHE-RSA-AES128-GCM-SHA256,2048,128
Server Temp Key:        ECDH X25519 253 bits
TLS Server Name:        kromgo.sko.ai

Document Path:          /query?metric=pods&format=badge
Document Length:        1122 bytes

Concurrency Level:      10
Time taken for tests:   6.542 seconds
Complete requests:      100
Failed requests:        34
   (Connect: 0, Receive: 0, Length: 34, Exceptions: 0)
Non-2xx responses:      33
Total transferred:      104707 bytes
HTML transferred:       78703 bytes
Requests per second:    15.29 [#/sec] (mean)
Time per request:       654.210 [ms] (mean)
Time per request:       65.421 [ms] (mean, across all concurrent requests)
Transfer rate:          15.63 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:       23   50  10.9     49      69
Processing:    22  577 306.1    549    1546
Waiting:       22  576 306.2    549    1546
Total:         62  626 307.2    604    1592

Percentage of the requests served within a certain time (ms)
  50%    604
  66%    697
  75%    764
  80%    825
  90%   1044
  95%   1268
  98%   1590
  99%   1592
 100%   1592 (longest request)
vasko@anchor ~ % ab -n 100 -c 10 'https://kromgo.sko.ai/query?metric=pods'             
This is ApacheBench, Version 2.3 <$Revision: 1903618 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking kromgo.sko.ai (be patient).....done


Server Software:        
Server Hostname:        kromgo.sko.ai
Server Port:            443
SSL/TLS Protocol:       TLSv1.2,ECDHE-RSA-AES128-GCM-SHA256,2048,128
Server Temp Key:        ECDH X25519 253 bits
TLS Server Name:        kromgo.sko.ai

Document Path:          /query?metric=pods
Document Length:        67 bytes

Concurrency Level:      10
Time taken for tests:   4.223 seconds
Complete requests:      100
Failed requests:        0
Total transferred:      39800 bytes
HTML transferred:       6700 bytes
Requests per second:    23.68 [#/sec] (mean)
Time per request:       422.305 [ms] (mean)
Time per request:       42.230 [ms] (mean, across all concurrent requests)
Transfer rate:          9.20 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:       25   49  12.4     48      77
Processing:    10  357 260.4    351    1135
Waiting:       10  357 260.6    351    1133
Total:         41  406 258.7    399    1165

Percentage of the requests served within a certain time (ms)
  50%    399
  66%    499
  75%    567
  80%    602
  90%    769
  95%    899
  98%   1163
  99%   1165
 100%   1165 (longest request)