fix: Do not require the google.api.http RPC option (#4973)
fix: Do not require the google.api.http RPC option (#4973)

If a method does not have the google.api.http option, return
an empty map from `ExtractParamsFromMethod()` instead of an
invalid-argument error.
googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp