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

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[colega]

Please note that this change has changed the behavior of ServerInHandle (gprc.InTapHandle option).

Previously, when ServerInHandle returned no error, the request would be processed, so any resource changes (like inflight requests counter) performed in ServerInHandle could be later undone though a stats handler.

Now, however, there's no such guarantee anymore.

I wonder if it would be possible to move this early return before the inTapHandle call?