[configgrpc] Add ClientConfig.EnhanceContextWithHeaders

[jade-guiton-dd]

Description

See related issue for context

Link to tracking issue

Resolves #12307

[codecov]

Codecov Report

Attention: Patch coverage is 10.00000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 91.38%. Comparing base (43087bd) to head (92064d1).
Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
config/configgrpc/configgrpc.go	0.00%	9 Missing ⚠️

❌ Your patch status has failed because the patch coverage (10.00%) 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   #12308      +/-   ##
==========================================
- Coverage   91.41%   91.38%   -0.04%     
==========================================
  Files         467      467              
  Lines       25583    25584       +1     
==========================================
- Hits        23387    23379       -8     
- Misses       1778     1787       +9     
  Partials      418      418              

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[jade-guiton-dd]

Turns out we can do this without an additional method with grpc.WithUnaryInterceptor, closing this