Setup protobuf project

[EtienneDx]

APIs will be defined in protobuf to enforce proper typings between the projects.

The protobuf messages should then be turned into both typescript and rust in the relevant projects.

As a starter message, the login API can be defined as follow:

message LoginRequest {
  string email = 1;
  string password = 2;
}

// TODO: double check if this can be written in a better way
message LoginResponse {
  bool success = 1;
  optional string token = 2;
}

[EtienneDx]

After multipl attemps, I gave up on protobuf and solved this problem using poem. See #25