feat: Add implementation of new AvailableComponents message

[mrsillydog]

Implements the specification added to opamp-spec in open-telemetry/opamp-spec#201

[codecov]

Codecov Report

Attention: Patch coverage is 95.38462% with 3 lines in your changes missing coverage. Please review.

Project coverage is 78.29%. Comparing base (e6fac32) to head (6cb83a6).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
client/internal/clientcommon.go	92.30%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #340      +/-   ##
==========================================
+ Coverage   77.81%   78.29%   +0.47%     
==========================================
  Files          25       25              
  Lines        2321     2386      +65     
==========================================
+ Hits         1806     1868      +62     
- Misses        408      410       +2     
- Partials      107      108       +1     

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[mrsillydog]

Comfortable moving this into Ready for Review - have successfully manually tested this implementation end-to-end with a custom build of the OpAMP Supervisor and OpAMP extension in open-telemetry/opentelemetry-collector-contrib.

[tigrannajaryan]

LGTM. Just one question on an edge case remaining.

[tigrannajaryan]

Thanks @mrsillydog !