feat[devtools]: add method for connecting backend with custom messaging protocol

[hoxyq]

Summary

RDT backend will now expose method connectWithCustomMessagingProtocol, which will be similar to the classic connectToDevTools one, but with few differences:

1. It delegates the communication management between frontend and backend to the owner (whos injecting RDT backend). Unlike the connectToDevTools, which is relying on websocket connection and receives host and port as an arguments.
2. It returns a callback, which can be used for unsubscribing the current backend instance from the global DevTools hook.

This is a prerequisite for any non-browser RDT integration, which is not designed to be based on websocket.