Communications: Community Updates

[techsmyth]

As a challenge / ecoverse admin I want to be able to message all members

Acceptance criteria

• [x] Able to send messages to a community, and all users that a member of that community receive the messages
• [x] Migration to latest matrix client sdk
• [x] Integrate types library that may now be available
• [x] Investigate is Dendrite is a drop in replacement for Synapse from the point of view of the matrix client sdk
• [x] Expand admin UI to allow ecoverse / challenge admins to be able to send messages to their community
• [x] Update messages to be in markdown
• [x] Subscriptions: in memory and limited scalability
• [x] Ability to delete existing messages them
• [x] Synapse admin container integrated into server-dev cluster

Additional Context

Read more about the investigation results investigation

[FloriSpoelstra]

Not sure if this epic also contains e-mail notification of new community messages. Would be great to have that (and people should of course also be able to unsubscribe from e-mail notifications).