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>

api4/user.go

@@ -3008,14 +3008,15 @@ func getThreadsForUser(c *Context, w http.ResponseWriter, r *http.Request) {
 	}
 
 	options := model.GetUserThreadsOpts{
-		Since:      0,
-		Before:     "",
-		After:      "",
-		PageSize:   uint64(c.Params.PerPage),
-		Unread:     false,
-		Extended:   false,
-		Deleted:    false,
-		TotalsOnly: false,
+		Since:       0,
+		Before:      "",
+		After:       "",
+		PageSize:    uint64(c.Params.PerPage),
+		Unread:      false,
+		Extended:    false,
+		Deleted:     false,
+		TotalsOnly:  false,
+		ThreadsOnly: false,
 	}
 
 	sinceString := r.URL.Query().Get("since")
@@ -3030,21 +3031,30 @@ func getThreadsForUser(c *Context, w http.ResponseWriter, r *http.Request) {
 
 	options.Before = r.URL.Query().Get("before")
 	options.After = r.URL.Query().Get("after")
+	totalsOnlyStr := r.URL.Query().Get("totalsOnly")
+	threadsOnlyStr := r.URL.Query().Get("threadsOnly")
+	options.TotalsOnly, _ = strconv.ParseBool(totalsOnlyStr)
+	options.ThreadsOnly, _ = strconv.ParseBool(threadsOnlyStr)
+
 	// parameters are mutually exclusive
 	if options.Before != "" && options.After != "" {
 		c.Err = model.NewAppError("api.getThreadsForUser", "api.getThreadsForUser.bad_params", nil, "", http.StatusBadRequest)
 		return
 	}
 
+	// parameters are mutually exclusive
+	if options.TotalsOnly && options.ThreadsOnly {
+		c.Err = model.NewAppError("api.getThreadsForUser", "api.getThreadsForUser.bad_only_params", nil, "", http.StatusBadRequest)
+		return
+	}
+
 	deletedStr := r.URL.Query().Get("deleted")
 	unreadStr := r.URL.Query().Get("unread")
 	extendedStr := r.URL.Query().Get("extended")
-	totalsOnlyStr := r.URL.Query().Get("totalsOnly")
 
 	options.Deleted, _ = strconv.ParseBool(deletedStr)
 	options.Unread, _ = strconv.ParseBool(unreadStr)
 	options.Extended, _ = strconv.ParseBool(extendedStr)
-	options.TotalsOnly, _ = strconv.ParseBool(totalsOnlyStr)
 
 	threads, err := c.App.GetThreadsForUser(c.Params.UserId, c.Params.TeamId, options)
 	if err != nil {