Core: Make application title customizable for WL (#22401)

* Core: Add custom app title

* Docs: Update White Labeling title customization

* Core: set back export for Branding types

pkg/api/dtos/index.go

@@ -17,6 +17,7 @@ type IndexViewData struct {
 	AppNameBodyClass        string
 	FavIcon                 string
 	AppleTouchIcon          string
+	AppTitle                string
 }
 
 type PluginCss struct {