Properly test long-standing WebSockets

[FabioPinheiro]

Some users are having problems using the WebSockets in the mediator.
We are still unable to replicate the problem.

So we need a way to try to consistently replicate the problem. @elribonazo may help about this.

WebSockets are essential for Live Mode feature in the pick up protocol

The mediator-test-suite also have a very limit number of tests for WebSockets
https://github.com/input-output-hk/didcomm-v2-mediator-test-suite/