[exporterhelper] Preserve request span context in the persistent queue

[dmitryax]

This change makes it possible to propagate span context through the Collector with enable persistent queue.

Currently, it is behind the exporter.PersistRequestContext feature gate, which can be enabled by adding --feature-gates=exporter.PersistRequestContext to the collector command line. An exporter buffer stored by a previous version of the collector (or by a collector with the feature gate disabled) can be read by a newer collector with the feature enabled. However, the reverse is not supported: a buffer stored by a newer collector with the feature enabled cannot be read by an older collector (or by a collector with the feature gate disabled).

Resolves https://github.com/open-telemetry/opentelemetry-collector/issues/11740

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 60.51502% with 92 lines in your changes missing coverage. Please review.

Project coverage is 91.28%. Comparing base (d800ad3) to head (bf58132). Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
...exporterhelper/internal/persistentqueue/meta.pb.go	21.00%	77 Missing and 2 partials :warning:
...xporterhelper/internal/persistentqueue/encoding.go	89.28%	8 Missing and 4 partials :warning:
...rterhelper/internal/queuebatch/persistent_queue.go	90.00%	0 Missing and 1 partial :warning:

:x: Your patch status has failed because the patch coverage (60.51%) 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   #13176      +/-   ##
==========================================
- Coverage   91.28%   91.28%   -0.01%     
==========================================
  Files         510      512       +2     
  Lines       28725    28844     +119     
==========================================
+ Hits        26223    26330     +107     
- Misses       1988     1996       +8     
- Partials      514      518       +4     

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[dmitryax]

@bogdandrutu @jmacd here is another approach that doesn't involve the custom encoding but introduces new public module pdata/xpdata/request which provides access to the pdata protobuf to built a wrapper on top of it https://github.com/open-telemetry/opentelemetry-collector/pull/13188

[dmitryax]

Closing in favor of https://github.com/open-telemetry/opentelemetry-collector/pull/13188