[exporterhelper] Support context marshaling/unmarshaling in the persistent queue

[dmitryax]

TODOs:

• Break down into mergable PRs
• Metadata keys support

[codecov]

Codecov Report

Attention: Patch coverage is 60.94891% with 107 lines in your changes missing coverage. Please review.

Project coverage is 91.22%. Comparing base (d800ad3) to head (156db27).
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 ⚠️
...xporterhelper/internal/persistentqueue/encoding.go	87.70%	10 Missing and 5 partials ⚠️
pdata/plog/pb.go	0.00%	3 Missing ⚠️
pdata/pmetric/pb.go	0.00%	3 Missing ⚠️
pdata/pprofile/pb.go	0.00%	3 Missing ⚠️
pdata/ptrace/pb.go	0.00%	3 Missing ⚠️
...rterhelper/internal/queuebatch/persistent_queue.go	90.00%	0 Missing and 1 partial ⚠️

❌ Your patch status has failed because the patch coverage (60.94%) 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   #13166      +/-   ##
==========================================
- Coverage   91.28%   91.22%   -0.07%     
==========================================
  Files         510      512       +2     
  Lines       28725    28901     +176     
==========================================
+ Hits        26223    26366     +143     
- Misses       1988     2015      +27     
- Partials      514      520       +6     

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