Add proto3 optional support

[icepaco]

Hi, I am getting this error :
google/storage/control/v2/storage_control.proto: is a proto3 file that contains optional fields, but code generator protoc-gen-grpc hasn't been updated to support optional fields in proto3. Please ask the owner of this code generator to support proto3 optional.

Running on : https://github.com/googleapis/googleapis/blob/master/google/storage/control/v2/storage_control.proto

Is it possible to add the support for proto3 optional ?

Thank you !