We need to review the current user docs for the Communication subsystem and implemented providers, and update/add missing features as necessary.

Note: This will also need to include creating a diagram outlining potential data flows within/between systems for the Matrix provider, and information relating to this, which will assist organisations who have data privacy obligations that may be affected by that provider (see michaelh for more info).

Doc Link: https://docs.moodle.org/403/en/Communication