Support client heartbeat

[haoqixu]

Implement spec change open-telemetry/opamp-spec#190

[codecov]

Codecov Report

Attention: Patch coverage is 88.37209% with 5 lines in your changes missing coverage. Please review.

Project coverage is 77.27%. Comparing base (536037b) to head (c451416).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/certs.go	0.00%	3 Missing ⚠️
client/internal/receivedprocessor.go	50.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #296      +/-   ##
==========================================
+ Coverage   77.24%   77.27%   +0.02%     
==========================================
  Files          25       25              
  Lines        1692     1729      +37     
==========================================
+ Hits         1307     1336      +29     
- Misses        282      286       +4     
- Partials      103      107       +4     

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[haoqixu]

@jaronoff97, considering you are the author of open-telemetry/opamp-spec#190, you might find this PR of interest and perhaps may want to review it.

[jaronoff97]

just one thought, otherwise this looks great.

[tigrannajaryan]

Thanks @haoqixu !