r0.6.1 support: /rooms/:roomId/aliases endpoint (#9224)

[MSC2432](matrix-org/matrix-spec-proposals#2432) added this endpoint originally but it has since been included in the spec for nearly a year. 

This is progress towards #8334

changelog.d/9224.feature

@@ -0,0 +1 @@
+Add new endpoint `/_matrix/client/r0/rooms/{roomId}/aliases` from Client-Server API r0.6.1 (previously [MSC2432](https://github.com/matrix-org/matrix-doc/pull/2432)).

synapse/rest/client/v1/room.py

@@ -910,7 +910,7 @@ class RoomAliasListServlet(RestServlet):
             r"^/_matrix/client/unstable/org\.matrix\.msc2432"
             r"/rooms/(?P<room_id>[^/]*)/aliases"
         ),
-    ]
+    ] + list(client_patterns("/rooms/(?P<room_id>[^/]*)/aliases$", unstable=False))
 
     def __init__(self, hs: "HomeServer"):
         super().__init__()

tests/rest/client/v1/test_rooms.py

@@ -1880,8 +1880,7 @@ def _get_aliases(self, access_token: str, expected_code: int = 200) -> JsonDict:
         """Calls the endpoint under test. returns the json response object."""
         channel = self.make_request(
             "GET",
-            "/_matrix/client/unstable/org.matrix.msc2432/rooms/%s/aliases"
-            % (self.room_id,),
+            "/_matrix/client/r0/rooms/%s/aliases" % (self.room_id,),
             access_token=access_token,
         )
         self.assertEqual(channel.code, expected_code, channel.result)