feat: add missing error consumer setter on connector

[petragabriela]

Currently, there is no way to receive and/or handle setup rejection errors because the error consumer of the RSocketConnector is always null

Motivation:

The connect function of the RSocketConnector sets the errorConsumer while the receiveFrame function of the RSocketRequester passes an error frame to the errorConsumer to handle the error. The problem is that the _errorConsumer of the RSocketConnecter has no setter and will always be null. So, users will not be able to receive and/or handle the error, for example when they receive a setup rejection error.

Modifications:

Adds a setter for the RSocketConnector's error consumer.

Result:

Now users can receive & handle setup errors correctly