Add /_dendrite/admin/evacuateRoom/{roomID} (#2401)

* Add new endpoint to allow admins to evacuate the local server from the room

* Guard endpoint

* Use right prefix

* Auth API

* More useful return error rather than a panic

* More useful return value again

* Update the path

* Try using inputer instead

* oh provide the config

* Try that again

* Return affected user IDs

* Don't create so many forward extremities

* Add missing `Path` to name

Co-authored-by: Till <2353100+S7evinK@users.noreply.github.com>

clientapi/clientapi.go

@@ -36,6 +36,7 @@ func AddPublicRoutes(
 	process *process.ProcessContext,
 	router *mux.Router,
 	synapseAdminRouter *mux.Router,
+	dendriteAdminRouter *mux.Router,
 	cfg *config.ClientAPI,
 	federation *gomatrixserverlib.FederationClient,
 	rsAPI roomserverAPI.RoomserverInternalAPI,
@@ -62,7 +63,8 @@ func AddPublicRoutes(
 	}
 
 	routing.Setup(
-		router, synapseAdminRouter, cfg, rsAPI, asAPI,
+		router, synapseAdminRouter, dendriteAdminRouter,
+		cfg, rsAPI, asAPI,
 		userAPI, userDirectoryProvider, federation,
 		syncProducer, transactionsCache, fsAPI, keyAPI,
 		extRoomsProvider, mscCfg, natsClient,