feat: support periodic ping to principal for keeping connection alive

[jparsai]

This PR is to introduce a configurable periodic ping to keep connection alive between agent and principal using grpc keepalive feature.

By default it is disabled and to enable it you need to set value of keep-alive-ping-interval in startup script or set env variable KEEP_ALIVE_PING_INTERVAL at agent side and at principal side you have to set value of wait-duration-for-agent-ping in startup script or set value of env variable WAIT_DURATION_FOR_AGENT_PING .

Fixes #171

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 25.00000% with 39 lines in your changes missing coverage. Please review.

Project coverage is 48.59%. Comparing base (cd3dc15) to head (032b731).

Files with missing lines	Patch %	Lines
pkg/client/remote.go	38.88%	10 Missing and 1 partial ⚠️
cmd/agent/main.go	0.00%	9 Missing ⚠️
cmd/principal/main.go	0.00%	8 Missing ⚠️
principal/options.go	0.00%	6 Missing ⚠️
principal/listen.go	54.54%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #288      +/-   ##
==========================================
- Coverage   48.79%   48.59%   -0.20%     
==========================================
  Files          73       73              
  Lines        6400     6451      +51     
==========================================
+ Hits         3123     3135      +12     
- Misses       3017     3054      +37     
- Partials      260      262       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[chetan-rns]

gRPC has support for configuring keepalives. Do you think we should use it?

https://grpc.io/docs/guides/keepalive/

[jparsai]

gRPC has support for configuring keepalives. Do you think we should use it?

https://grpc.io/docs/guides/keepalive/

@chetan-rns addressed your comment PTAL