MM-56071: Track multiple threads (#25775)

We can have 2 types of threads open at the same time. One from
the thread view, and another from RHS.

We add another variable to distinguish between the 2 states.

In future, if we have the ability for more than 2 threads, then
we would need to track by threadID.

https://mattermost.atlassian.net/browse/MM-56071

```release-note
NONE
```

server/public/model/websocket_client.go

@@ -343,9 +343,10 @@ func (wsc *WebSocketClient) UpdateActiveTeam(teamID string) {
 }
 
 // UpdateActiveThread sets the channel id of the current thread that the user is in.
-func (wsc *WebSocketClient) UpdateActiveThread(channelID string) {
+func (wsc *WebSocketClient) UpdateActiveThread(isThreadView bool, channelID string) {
 	data := map[string]any{
 		"thread_channel_id": channelID,
+		"is_thread_view":    isThreadView,
 	}
 	wsc.SendMessage(string(WebsocketPresenceIndicator), data)
 }