Transfer related groups on room upgrade (#4990)

Transfers the m.room.related_groups state event on room upgrade.

changelog.d/4990.bugfix

@@ -0,0 +1 @@
+Transfer related groups on room upgrade.

synapse/api/constants.py

@@ -69,6 +69,7 @@ class EventTypes(object):
     Redaction = "m.room.redaction"
     ThirdPartyInvite = "m.room.third_party_invite"
     Encryption = "m.room.encryption"
+    RelatedGroups = "m.room.related_groups"
 
     RoomHistoryVisibility = "m.room.history_visibility"
     CanonicalAlias = "m.room.canonical_alias"

synapse/handlers/room.py

@@ -280,6 +280,7 @@ class RoomCreationHandler(BaseHandler):
             (EventTypes.RoomAvatar, ""),
             (EventTypes.Encryption, ""),
             (EventTypes.ServerACL, ""),
+            (EventTypes.RelatedGroups, ""),
         )
 
         old_room_state_ids = yield self.store.get_filtered_current_state_ids(