[MM-55143] Disallow reacting with an emoji that does not exist, limit the total number of unique reactions per post (#25331)

* [MM-55143] Disallow reacting with an emoji that does not exist

* WIP for server limit on emoji reactions

* WIP

* Implement default limit of 25 unique emoji reactions

* Add modal for reaction limit

* Fix test

* PR feedback

* Fix i18n

* Update admin string

* Merge'd

* Fixing some issues, check limits correctly based on other users reactions

* Fix typos

* Fix lint/test

* Add tests, fix other tests

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

e2e-tests/playwright/support/server/default_config.ts

@@ -179,6 +179,7 @@ const defaultServerConfig: AdminConfig = {
         EnableCustomGroups: true,
         SelfHostedPurchase: true,
         AllowSyncedDrafts: true,
+        UniqueEmojiReactionLimitPerPost: 25,
         RefreshPostStatsRunTime: '00:00',
     },
     TeamSettings: {