MM-28338 Fix Combined system messages (#22608)

* Web App -> Monorepo

* Update message data

* update snapshots

* update tests

* update tests, add null filter for userIds.

* Revert "update snapshots"

This reverts commit 4b3f5b192d355866bca978cfc708352bb5218694.

* Remove not related tests

* Update post_list

* Update test (removing usernames for UserIds)

* Update webapp/channels/src/packages/mattermost-redux/src/utils/post_list.ts

better readability.

Co-authored-by: Harrison Healey <harrisonmhealey@gmail.com>

* remove unnecessary tests.

---------

Co-authored-by: Harrison Healey <harrisonmhealey@gmail.com>
Co-authored-by: Mattermost Build <build@mattermost.com>

webapp/platform/types/src/posts.ts

@@ -204,3 +204,9 @@ export type PostAnalytics = {
     requested_ack?: boolean;
     persistent_notifications?: boolean;
 }
+export type ActivityEntry = {
+    postType: Post['type'];
+    actorId: string[];
+    userIds: string[];
+    usernames: string[];
+}