[MM-37013] Async job to fix CRT channel unreads (#18340)

Summary
The addition of the TotalMsgCountRoot and MsgCountRoot columns to support CRT caused several issues with previously read threads and channels being marked as unread. Previously we attempted to fix this purely in a SQL migration [MM-35345][MM-35494] fixes for incorrect mentions and unreads for threads and channels #17803 but that turned out to be too heavy and it was decided to break up some of the fixes into async jobs.
This PR implements an async job to mark channels as read if there are no user posts since the last time the user viewed the channel. 

Ticket Link
https://mattermost.atlassian.net/browse/MM-37013

store/retrylayer/retrylayer.go

@@ -1129,6 +1129,27 @@ func (s *RetryLayerChannelStore) GetByNames(team_id string, names []string, allo
 
 }
 
+func (s *RetryLayerChannelStore) GetCRTUnfixedChannelMembershipsAfter(channelID string, userID string, count int) ([]model.ChannelMember, error) {
+
+	tries := 0
+	for {
+		result, err := s.ChannelStore.GetCRTUnfixedChannelMembershipsAfter(channelID, userID, count)
+		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 *RetryLayerChannelStore) GetChannelCounts(teamID string, userID string) (*model.ChannelCounts, error) {
 
 	tries := 0
@@ -6385,6 +6406,27 @@ func (s *RetryLayerPostStore) GetSingle(id string, inclDeleted bool) (*model.Pos
 
 }
 
+func (s *RetryLayerPostStore) GetUniquePostTypesSince(channelId string, timestamp int64) ([]string, error) {
+
+	tries := 0
+	for {
+		result, err := s.PostStore.GetUniquePostTypesSince(channelId, timestamp)
+		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 *RetryLayerPostStore) HasAutoResponsePostByUserSince(options model.GetPostsSinceOptions, userId string) (bool, error) {
 
 	tries := 0