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 45.76271% with 32 lines in your changes missing coverage. Please review.

Project coverage is 77.01%. Comparing base (e6fac32) to head (26a7996).

Files with missing lines	Patch %	Lines
client/internal/clientcommon.go	24.24%	23 Missing and 2 partials ⚠️
client/internal/clientstate.go	80.00%	2 Missing and 1 partial ⚠️
client/httpclient.go	0.00%	2 Missing ⚠️
client/wsclient.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #340      +/-   ##
==========================================
- Coverage   77.81%   77.01%   -0.80%     
==========================================
  Files          25       25              
  Lines        2321     2380      +59     
==========================================
+ Hits         1806     1833      +27     
- Misses        408      437      +29     
- Partials      107      110       +3     

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