[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>

server/channels/store/retrylayer/retrylayer.go

@@ -8474,6 +8474,27 @@ func (s *RetryLayerReactionStore) DeleteOrphanedRowsByIds(r *model.RetentionIdsF
 
 }
 
+func (s *RetryLayerReactionStore) ExistsOnPost(postId string, emojiName string) (bool, error) {
+
+	tries := 0
+	for {
+		result, err := s.ReactionStore.ExistsOnPost(postId, emojiName)
+		if err == nil {
+			return result, nil
+		}
+		if !isRepeatableError(err) {
+			return result, err
+		}
+		tries++
+		if tries >= 3 {
+			err = errors.Wrap(err, "giving up after 3 consecutive repeatable transaction failures")
+			return result, err
+		}
+		timepkg.Sleep(100 * timepkg.Millisecond)
+	}
+
+}
+
 func (s *RetryLayerReactionStore) GetForPost(postID string, allowFromCache bool) ([]*model.Reaction, error) {
 
 	tries := 0
@@ -8516,6 +8537,27 @@ func (s *RetryLayerReactionStore) GetForPostSince(postId string, since int64, ex
 
 }
 
+func (s *RetryLayerReactionStore) GetUniqueCountForPost(postId string) (int, error) {
+
+	tries := 0
+	for {
+		result, err := s.ReactionStore.GetUniqueCountForPost(postId)
+		if err == nil {
+			return result, nil
+		}
+		if !isRepeatableError(err) {
+			return result, err
+		}
+		tries++
+		if tries >= 3 {
+			err = errors.Wrap(err, "giving up after 3 consecutive repeatable transaction failures")
+			return result, err
+		}
+		timepkg.Sleep(100 * timepkg.Millisecond)
+	}
+
+}
+
 func (s *RetryLayerReactionStore) PermanentDeleteBatch(endTime int64, limit int64) (int64, error) {
 
 	tries := 0