Support code generation for proto definitions utilizing experimental features

[Archisman-Mridha]

Is your feature request related to a problem? Please describe.
Programmatic code generation is not working if I use experimental gRPC features like the optional keyword in proto definition files.

Describe the solution you'd like
To generate code for proto files utilizing experimental features, we need to add --experimental_allow_proto3_optional to the protoc command while generating code. Please provide an option where we can enable or disable this flag in the compile_grpc_protos method.

Describe alternatives you've considered
I couldn't find any alternative to get through this problem.

Additional context
This is the error I am getting when I am trying to generate code -

This file contains proto3 optional fields, but --experimental_allow_proto3_optional was not set.

[Archisman-Mridha]

Instead of using the optional field, I tried this -

import "google/protobuf/wrappers.proto";

message RegistrationResponse {
    google.protobuf.StringValue error= 1;

    string jwt= 2;
}