Add delete room admin endpoint (#7613)

The Delete Room admin API allows server admins to remove rooms from server
and block these rooms.
`DELETE /_synapse/admin/v1/rooms/<room_id>`
It is a combination and improvement of "[Shutdown room](https://github.com/matrix-org/synapse/blob/develop/docs/admin_api/shutdown_room.md)" and "[Purge room](https://github.com/matrix-org/synapse/blob/develop/docs/admin_api/purge_room.md)" API.

Fixes: #6425 

It also fixes a bug in [synapse/storage/data_stores/main/room.py](synapse/storage/data_stores/main/room.py) in ` get_room_with_stats`.
It should return `None` if the room is unknown. But it returns an `IndexError`.
901b1fa561/synapse/storage/data_stores/main/room.py (L99-L105)

Related to:
- #5575
- https://github.com/Awesome-Technologies/synapse-admin/issues/17

Signed-off-by: Dirk Klimpel dirk@klimpel.org

synapse/storage/data_stores/main/room.py

@@ -118,7 +118,12 @@ class RoomWorkerStore(SQLBaseStore):
                 WHERE room_id = ?
                 """
             txn.execute(sql, [room_id])
-            res = self.db.cursor_to_dict(txn)[0]
+            # Catch error if sql returns empty result to return "None" instead of an error
+            try:
+                res = self.db.cursor_to_dict(txn)[0]
+            except IndexError:
+                return None
+
             res["federatable"] = bool(res["federatable"])
             res["public"] = bool(res["public"])
             return res