Cherry-pick #8439 to v1.74 release branch

[dfawley]

RELEASE NOTES:

• server: allow 0s grpc-timeout header values, which older gRPC-Java versions could send

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 11 lines in your changes missing coverage. Please review.

Project coverage is 82.40%. Comparing base (1787f94) to head (de39ffe).
Report is 1 commits behind head on v1.74.x.

Files with missing lines	Patch %	Lines
internal/transport/http2_server.go	0.00%	10 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           v1.74.x    #8440      +/-   ##
===========================================
- Coverage    82.50%   82.40%   -0.11%     
===========================================
  Files          414      414              
  Lines        40420    40428       +8     
===========================================
- Hits         33347    33313      -34     
- Misses        5728     5758      +30     
- Partials      1345     1357      +12     

Files with missing lines	Coverage Δ
internal/transport/http_util.go	94.44% <ø> (-0.07%)	⬇️
internal/transport/http2_server.go	90.68% <0.00%> (-0.37%)	⬇️

... and 20 files with indirect coverage changes

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