[Gekidou] Multi-Server support UI (#5912)

* Multi-Server support UI

* feedback review

* Apply suggestions from code review

Co-authored-by: Avinash Lingaloo <avinashlng1080@gmail.com>

Co-authored-by: Avinash Lingaloo <avinashlng1080@gmail.com>

types/database/subscriptions/index.ts

@@ -0,0 +1,13 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+import type {Subscription} from 'rxjs';
+
+export type UnreadMessages = {
+    mentions: number;
+    unread: boolean;
+};
+
+export type UnreadSubscription = UnreadMessages & {
+    subscription?: Subscription;
+};