feat: Add opt_args to common_proto_library. (#3191)
feat: Add opt_args to common_proto_library. (#3191)

This is to suport <plugin_name>_opt command line args for protoc with a <plugin>.
googleapis/gapic-generator,googleapis/gapic-generator,googleapis/gapic-generator,googleapis/gapic-generator,googleapis/gapic-generator,googleapis/gapic-generator,googleapis/gapic-generator