Bytes based batching for metrics

[iblancasa]

Description

This PR implements serialized bytes based batching for metrics.

Link to tracking issue

#3262

Continuation of #12299 made by @sfc-gh-sili.

[iblancasa]

#12519 (review)

[codecov]

Codecov Report

Attention: Patch coverage is 91.63498% with 22 lines in your changes missing coverage. Please review.

Project coverage is 92.17%. Comparing base (e43c36c) to head (b257e39).

Files with missing lines	Patch %	Lines
pdata/pmetric/pb.go	0.00%	14 Missing ⚠️
exporter/exporterhelper/metrics_batch.go	96.01%	7 Missing and 1 partial ⚠️

❌ Your patch check has failed because the patch coverage (91.63%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12550      +/-   ##
==========================================
- Coverage   92.21%   92.17%   -0.04%     
==========================================
  Files         469      470       +1     
  Lines       25368    25537     +169     
==========================================
+ Hits        23392    23539     +147     
- Misses       1568     1589      +21     
- Partials      408      409       +1     

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[dmitryax]

Thanks, @iblancasa. Please adopt the recent changes made in #12548