MM-40148: threadsOnly query param for user threads (#19833)

* MM-40148: threadsOnly query param for user threads

Currently we always calculate counts when fetching user threads.
Those counts include total, unread replies, and unread mentions,
and are potentially expensive to calculate.

This commit adds a new query param 'threadsOnly' which won't calculate
any counts and just return threads.

Co-authored-by: koox00 <3829551+koox00@users.noreply.github.com>
Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/user.go

@@ -2296,35 +2296,37 @@ func (a *App) GetThreadsForUser(userID, teamID string, options model.GetUserThre
 	var result model.Threads
 	var eg errgroup.Group
 
-	eg.Go(func() error {
-		totalUnreadThreads, err := a.Srv().Store.Thread().GetTotalUnreadThreads(userID, teamID, options)
-		if err != nil {
-			return errors.Wrapf(err, "failed to count unread threads for user id=%s", userID)
-		}
-		result.TotalUnreadThreads = totalUnreadThreads
+	if !options.ThreadsOnly {
+		eg.Go(func() error {
+			totalUnreadThreads, err := a.Srv().Store.Thread().GetTotalUnreadThreads(userID, teamID, options)
+			if err != nil {
+				return errors.Wrapf(err, "failed to count unread threads for user id=%s", userID)
+			}
+			result.TotalUnreadThreads = totalUnreadThreads
 
-		return nil
-	})
+			return nil
+		})
 
-	eg.Go(func() error {
-		totalCount, err := a.Srv().Store.Thread().GetTotalThreads(userID, teamID, options)
-		if err != nil {
-			return errors.Wrapf(err, "failed to count threads for user id=%s", userID)
-		}
-		result.Total = totalCount
+		eg.Go(func() error {
+			totalCount, err := a.Srv().Store.Thread().GetTotalThreads(userID, teamID, options)
+			if err != nil {
+				return errors.Wrapf(err, "failed to count threads for user id=%s", userID)
+			}
+			result.Total = totalCount
 
-		return nil
-	})
+			return nil
+		})
 
-	eg.Go(func() error {
-		totalUnreadMentions, err := a.Srv().Store.Thread().GetTotalUnreadMentions(userID, teamID, options)
-		if err != nil {
-			return errors.Wrapf(err, "failed to count threads for user id=%s", userID)
-		}
-		result.TotalUnreadMentions = totalUnreadMentions
+		eg.Go(func() error {
+			totalUnreadMentions, err := a.Srv().Store.Thread().GetTotalUnreadMentions(userID, teamID, options)
+			if err != nil {
+				return errors.Wrapf(err, "failed to count threads for user id=%s", userID)
+			}
+			result.TotalUnreadMentions = totalUnreadMentions
 
-		return nil
-	})
+			return nil
+		})
+	}
 
 	if !options.TotalsOnly {
 		eg.Go(func() error {