Allow passing the server config in the msg

[skylord123]

Currently each node requires you to select the matrix client to use. It would be cool if you could set it to msg.matrixclient and select the server based on the msg input.

This would make flows easier to re-use for multiple matrix accounts running in a single instance (no more duping is the idea).

Could either use the config node's ID (could be more difficult though) or just use the client's userId (probably the preferred way to do this).