MM-29703 Mark threads as read when channels are marked (#15994)

Co-authored-by: Jesús Espino <jespinog@gmail.com>

app/notification.go

@@ -184,7 +184,7 @@ func (a *App) SendNotifications(post *model.Post, team *model.Team, channel *mod
 		umc := make(chan *model.AppError, 1)
 		go func(userId string) {
 			defer close(umc)
-			nErr := a.Srv().Store.Channel().IncrementMentionCount(post.ChannelId, userId)
+			nErr := a.Srv().Store.Channel().IncrementMentionCount(post.ChannelId, userId, *a.Config().ServiceSettings.ThreadAutoFollow)
 			if nErr != nil {
 				umc <- model.NewAppError("SendNotifications", "app.channel.increment_mention_count.app_error", nil, nErr.Error(), http.StatusInternalServerError)
 				return