Support only E2E or public rooms on my homeserver

[lofidevops]

User story: I am a well-intentioned sysadmin. I want to host a homeserver on the Internet, so that I can help strangers communicate without myself being coerced into reporting user activity.

Suggested solution: Configure the homeserver so that only two room types are supported:

1. E2E rooms with limited access. Only end-users can see the contents of the room.
2. Cleartext rooms with public access. The conversation is stored in cleartext on my server, and anyone with the room URL can read the conversation.

Thus, cleartext rooms with limited access cannot be created or accessed from this homeserver. Users who need such rooms can use a different homeserver.

Rationale: https://code.puri.sm/purist/services/wiki/pattern_trustworthy_service

[ara4n]

For context, i've been discussing this a bunch with @kwill already. From my pov, this is essentially the same as E2E-by-default as per the final stage of the E2E end-game meta-bug over at element-hq/element-web#6779.

This is effectively blocked on that bug. It also presupposes that we're going to make 1:1s / private groups / public rooms immutable (which has been proposed off the back of the Fractal hackfest anyway - https://github.com/matrix-org/matrix-doc/issues/1255).

[anoadragon453]

#7639 is related and allows you to force all new locally-created rooms to have E2EE enabled.