Easier way to find interaction by key in PrepareInteractionForVerification rpc of plugin

[fsahmad]

Writing a plugin with a custom transport and while writing the PrepareInteractionForVerification rpc implementation I found there's an interactionKey in the request message:

// Request to prepare an interaction for verification
message VerificationPreparationRequest {
  // Pact as JSON to use for the verification
  string pact = 1;
  // Interaction key for the interaction from the Pact that is being verified
  string interactionKey = 2;
  // Any data supplied by the user to verify the interaction
  google.protobuf.Struct config = 3;
}

The JSON sent is annotated with this interactionKey, but I was hoping to use the pactffi functions to parse the pact JSON instead of having to write my own parsing code.

For comparison, in the StartMockServer rpc I can do the following and use the pactffi functions to drill down further:

auto pact_json = request->pact();
auto pact = pactffi_parse_pact_json(pact_json.c_str());