[MM-17194] Add search channels for user in case the user doesn't have the list channels permission (#11706)

* [MM-17194] Add search channels for user in case the user doesn't have the list channels permission

* Add tests for the API layer and control the case of a user not being a team member

* Remove unnecessary empty line

api4/channel.go

@@ -746,12 +746,20 @@ func searchChannelsForTeam(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if !c.App.SessionHasPermissionToTeam(c.App.Session, c.Params.TeamId, model.PERMISSION_LIST_TEAM_CHANNELS) {
-		c.SetPermissionError(model.PERMISSION_LIST_TEAM_CHANNELS)
-		return
+	var channels *model.ChannelList
+	var err *model.AppError
+	if c.App.SessionHasPermissionToTeam(c.App.Session, c.Params.TeamId, model.PERMISSION_LIST_TEAM_CHANNELS) {
+		channels, err = c.App.SearchChannels(c.Params.TeamId, props.Term)
+	} else {
+		// If the user is not a team member, return a 404
+		if _, err = c.App.GetTeamMember(c.Params.TeamId, c.App.Session.UserId); err != nil {
+			c.Err = err
+			return
+		}
+
+		channels, err = c.App.SearchChannelsForUser(c.App.Session.UserId, c.Params.TeamId, props.Term)
 	}
 
-	channels, err := c.App.SearchChannels(c.Params.TeamId, props.Term)
 	if err != nil {
 		c.Err = err
 		return