PSMDB metrics exporter as sidecar

[chilagrow]

Refs openeverest/openeverest#1799.

This demonstrates how metrics can be exported via /metrics endpoint using side car.

[chilagrow]

kubectl -n everest exec psmdb-exporter-rs0-0 -- curl localhost:9216/metrics
...
# HELP go_sched_gomaxprocs_threads The current runtime.GOMAXPROCS setting, or the number of operating system threads that can execute user-level Go code simultaneously. Sourced from /sched/gomaxprocs:threads.
# TYPE go_sched_gomaxprocs_threads gauge
go_sched_gomaxprocs_threads 14
# HELP go_threads Number of OS threads created.
# TYPE go_threads gauge
go_threads 11
# HELP mongodb_fcv_feature_compatibility_version Feature compatibility version
# TYPE mongodb_fcv_feature_compatibility_version gauge
mongodb_fcv_feature_compatibility_version{version="8.0"} 8
# HELP mongodb_up Whether MongoDB is up.
# TYPE mongodb_up gauge
mongodb_up{cluster_role="mongod"} 1
# HELP process_cpu_seconds_total Total user and system CPU time spent in seconds.
# TYPE process_cpu_seconds_total counter
process_cpu_seconds_total 0.03
# HELP process_max_fds Maximum number of open file descriptors.
# TYPE process_max_fds gauge
process_max_fds 1.048576e+06
# HELP process_network_receive_bytes_total Number of bytes received by the process over the network.
# TYPE process_network_receive_bytes_total counter
process_network_receive_bytes_total 3.523682e+06
# HELP process_network_transmit_bytes_total Number of bytes sent by the process over the network.
# TYPE process_network_transmit_bytes_total counter
process_network_transmit_bytes_total 3.690337e+06
# HELP process_open_fds Number of open file descriptors.
# TYPE process_open_fds gauge
process_open_fds 13
# HELP process_resident_memory_bytes Resident memory size in bytes.
# TYPE process_resident_memory_bytes gauge
process_resident_memory_bytes 3.3107968e+07
# HELP process_start_time_seconds Start time of the process since unix epoch in seconds.
# TYPE process_start_time_seconds gauge
process_start_time_seconds 1.77018535928e+09
# HELP process_virtual_memory_bytes Virtual memory size in bytes.
# TYPE process_virtual_memory_bytes gauge
process_virtual_memory_bytes 1.292095488e+09
# HELP process_virtual_memory_max_bytes Maximum amount of virtual memory available in bytes.
# TYPE process_virtual_memory_max_bytes gauge
process_virtual_memory_max_bytes 1.8446744073709552e+19