[Commtest] add mock olm accounts, configure creating authenticated device

Summary:
To properly test WebSocket one device is not enough. We should send message from one device and receive it on another.
Adding two more, generated via local olm.

Depends on D9311

Test Plan: Run tests and make sure new credentials works.

Reviewers: michal, bartek, varun, jon

Reviewed By: michal, bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9312