feat: add knockroom api

[Decodetalkers]

add a knockRoom to connection.h

[KitsuneRal]

I'm afraid it's just a tad harder than just that.

[KitsuneRal]

You really should have read this comment before copying it from joinRoom()... provideRoom() creates a room in Join state by default - this is not the desired behaviour here.

Suggested change

	// with a sync yet. If the room object is not there, provideRoom() will
	// create it in Join state. finished() is used here instead of success()
	// to overtake clients that may add their own slots to finished().
	connect(job, &BaseJob::finished, this, [this, job] {
	if (job->status().good())
	provideRoom(job->roomId());
	// with a sync yet. If the room object is not there, provideRoom() will
	// create it in Knock state. finished() is used here instead of success()
	// to overtake clients that may add their own slots to finished().
	connect(job, &BaseJob::finished, this, [this, job] {
	if (job->status().good())
	provideRoom(job->roomId(), JoinState::Knock);

There's yet another potential problem here: provideRoom() was written with just three join states in mind, and I cannot figure off the top of my head how it will behave if the room is found but is not in the Leave state. The code of provideRoom() should be reviewed and possibly updated to make sure Quotient clients don't accidentally turn, e.g., already joined rooms into knock rooms (the homeserver won't allow that but the local state may be screwed).