MM-56060: Create base scaffolding for websocket pub-sub (#25654)

We create a new websocket action called "presence" which
can contain the active_channel and the active_team for a given
client connection.

On the client side, for every channel or team switch, we send
out this message.

https://mattermost.atlassian.net/browse/MM-56060

```release-note
NONE
```

webapp/platform/client/src/websocket.ts

@@ -355,7 +355,7 @@ export default class WebSocketClient {
         }
     }
 
-    sendMessage(action: string, data: any, responseCallback?: () => void) {
+    sendMessage(action: string, data: any, responseCallback?: (msg: any) => void) {
         const msg = {
             action,
             seq: this.responseSequence++,
@@ -382,6 +382,20 @@ export default class WebSocketClient {
         this.sendMessage('user_typing', data, callback);
     }
 
+    updateActiveChannel(channelId: string, callback?: (msg: any) => void) {
+        const data = {
+            channel_id: channelId,
+        };
+        this.sendMessage('presence', data, callback);
+    }
+
+    updateActiveTeam(teamId: string, callback?: (msg: any) => void) {
+        const data = {
+            team_id: teamId,
+        };
+        this.sendMessage('presence', data, callback);
+    }
+
     userUpdateActiveStatus(userIsActive: boolean, manual: boolean, callback?: () => void) {
         const data = {
             user_is_active: userIsActive,