Define an avatar field in the room response

proposals/3575-sync.md

@@ -133,6 +133,7 @@ An entire response looks like:
     // Room from room subscription
     "!sub1:bar": {
         "name": "Alice and Bob",
+       "avatar": "mxc://...",
         "initial": true,
         "required_state": [
           {"sender":"@alice:example.com","type":"m.room.create", "state_key":"", "content":{"creator":"@alice:example.com"}},
@@ -157,6 +158,7 @@ An entire response looks like:
     // rooms from list
     "!foo:bar": {
       "name": "The calculated room name",
+      "avatar": "mxc://...",
       "initial": true,
       "required_state": [
         {"sender":"@alice:example.com","type":"m.room.join_rules", "state_key":"", "content":{"join_rule":"invite"}},
@@ -504,6 +506,8 @@ The server will then return a `rooms` key which have the following fields:
     // the room ID
     "!foo:bar": {
       "name": "The calculated room name",
+      // The MXC URL of the room's avatar, or the string "none" if this room has no prescribed avatar.
+      "avatar": "mxc://...",
       // Flag which is set when this is the first time the server is sending this data on this connection.
       // Clients can use this flag to replace or update their local state. When there is an update, servers
       // MUST omit this flag entirely and NOT send "initial":false as this is wasteful on bandwidth. The