server: allow 0s grpc-timeout header values, as java is known to be able to send them

[dfawley]

grpc/grpc-java#12201 was recently created to prevent this, but older versions will still do it. This reverts our old behavior of allowing 0 second timeouts (pre- #8290).

I would propose that we do not revert the change in http_util and allow the RPC to instantly timeout instead of throw an internal error.

cc @ejona86

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 82.34%. Comparing base (a21e374) to head (3059358).
Report is 2 commits behind head on master.

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             @@
##           master    #8439      +/-   ##
==========================================
+ Coverage   82.26%   82.34%   +0.07%     
==========================================
  Files         414      414              
  Lines       40410    40418       +8     
==========================================
+ Hits        33243    33281      +38     
+ Misses       5796     5774      -22     
+ Partials     1371     1363       -8     

Files with missing lines	Coverage Δ
internal/transport/http_util.go	94.44% <ø> (-0.07%)	⬇️
internal/transport/http2_server.go	90.14% <0.00%> (-0.64%)	⬇️

... and 18 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.