MM-39041: expose TotalsOnly option (#18767)

Sending a request to GetThreadsForUser for a TotalsOnly
returns just the counts without any threads.

api4/user.go

@@ -2989,6 +2989,7 @@ func getThreadsForUser(c *Context, w http.ResponseWriter, r *http.Request) {
 		Unread:     false,
 		Extended:   false,
 		Deleted:    false,
+		TotalsOnly: false,
 	}
 
 	sinceString := r.URL.Query().Get("since")
@@ -3012,10 +3013,12 @@ func getThreadsForUser(c *Context, w http.ResponseWriter, r *http.Request) {
 	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 {