Migrade from github.com/golang/protobuf to google.golang.org/protobuf

[govargo]

I found that the github.com/golang/protobuf will be deprecated in the future.

WARNING: Package "github.com/golang/protobuf/protoc-gen-go/generator" is deprecated.
        A future release of golang/protobuf will delete this package,
        which has long been excluded from the compatibility promise.

Related issue for agones: googleforgames/agones#2786
Related issue for open-match: googleforgames/open-match#1443

We need to change from github.com/golang/protobuf to google.golang.org/protobuf.