gateway add allowUnknownFields option

[jaronnie]

When I use the gateway framework, I found that when there is a field in the request body that does not exist in proto, an error will be reported as follows: error getting request data: message type hellopb.SayHelloRequest has no known field named name. So adding an option allowUnknownFields to fix it and passing in the value when calling the underlying grpcurl can solve the problem.

[jaronnie]

@kevwan help review

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.03%. Comparing base (8690859) to head (2ead9b0).
Report is 145 commits behind head on master.

Additional details and impacted files

Files with missing lines	Coverage Δ
gateway/internal/requestparser.go	100.00% <100.00%> (ø)
gateway/server.go	72.27% <100.00%> (+3.36%)	⬆️

... and 253 files with indirect coverage changes

[jaronnie]

@kevwan really need this option, thanks