bridge command should be callable without login

[shukon]

Thanks so much @maltee1 for the relaybot/bridge option introduced here.

It is currently possible to bridge rooms from the relaybot account or any other logged in account. It would be nice to have the bridging available without having to log in though. So any user with relay-permissions could bridge a room, given they have the ACL necessary to do it. Also, a specified relaybot is invited, but relay-mode not enabled on bridging (though I think #295 takes care of that(?)).

What I'd imagine/expect from bridging behaviour, if I'm looking at the telegram bridge command:

• Any user with permission to bridge a group should be able to use the !signal bridge command without logging in (currently the command-handler checks the needs_auth).
• The relaybot should reply on the signal-side to the !signal id command, so I don't have to get the id by logging into the relaybot-matrix-account.
• Using the !signal bridge <signal_id> <matrix_room_id> command should invite the specified relaybot and set relaymode automatically.

I'm fine with this being out of scope, but asking doesn't hurt 😊 it would enable users to bridge signal groups/communities without giving up all their data sovereignty / mirroring all their data to the matrix and without admin intervention.

[maltee1]

I do think this should be possible (along with a create command). The unfinished invite command was also intended for groups where most or all users don't have a signal account but need to manage the signal side. I might implement this if @tulir agrees to merge it once it's ready. I'm currently really busy though, so I won't do it any time soon.