Attempt at implementing https://dev.louiz.org/issues/3401
Adds a command that invites people into a newly created room (with a randomly generated name), on a configured muc component, or the one available on the user's domain.
I implemented a
/impromptu command, usable everywhere in poezio, that takes JIDs as argument and create a new room.
I also changed
/invite so that it can be used in 1:1 tabs.