monitor data format error by prometheus

[Corey-Wang]

Describe the bug
/monitor/bal_table_status?format=prometheus
/monitor/host_table_status?format=prometheus
/monitor/proxy_mem_stat?format=prometheus

response data is not prometheus format

example:
/monitor/bal_table_status?format=prometheus
response

[kwanhur]

From the monitorHandlers, we can known that host_table_status host_table_version cluster_table_version bal_table_status bal_table_version module_status module_handlers proxy_mem_stat non-support prometheus format, because they're not state related monitor items.