[API/SDK] feat: exemplar filters

[proost]

Fixes

• Is support for exemplars still experimental/preview? #4178
• Update exemplar and remove ExemplarFilter interface #2526

Changes

Complete exemplar filter.

This changes accompany breaking change. When I read versioning policy, flagged feature is unstable, so API breaking change is accepted, right?

I tried to abstract filte logic into FilteredExemplarReservoir to avoid filtering logic scattered to metric storage.

Please provide a brief description of the changes here.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.96%. Comparing base (a56f0e2) to head (34cc7e6).

Files with missing lines	Patch %	Lines
api/include/opentelemetry/trace/context.h	63.64%	4 Missing ⚠️
...sdk/metrics/exemplar/filtered_exemplar_reservoir.h	88.89%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4191      +/-   ##
==========================================
+ Coverage   82.89%   82.96%   +0.07%     
==========================================
  Files         405      406       +1     
  Lines       17292    17308      +16     
==========================================
+ Hits        14332    14357      +25     
+ Misses       2960     2951       -9     

Files with missing lines	Coverage Δ
...ude/opentelemetry/sdk/metrics/exemplar/reservoir.h	100.00% <ø> (ø)
...entelemetry/sdk/metrics/exemplar/reservoir_utils.h	100.00% <100.00%> (ø)
...telemetry/sdk/metrics/state/async_metric_storage.h	95.24% <100.00%> (+4.33%)	⬆️
...ntelemetry/sdk/metrics/state/sync_metric_storage.h	89.86% <100.00%> (+7.58%)	⬆️
sdk/src/logs/logger.cc	93.55% <100.00%> (+3.83%)	⬆️
sdk/src/metrics/exemplar/reservoir.cc	75.00% <100.00%> (+8.34%)	⬆️
sdk/src/metrics/meter.cc	81.36% <ø> (ø)
...sdk/metrics/exemplar/filtered_exemplar_reservoir.h	88.89% <88.89%> (ø)
api/include/opentelemetry/trace/context.h	82.61% <63.64%> (-17.39%)	⬇️

... and 1 file with indirect coverage changes

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