Ensure all back office controllers are plugin controllers and use constant

src/Umbraco.Web.BackOffice/Controllers/MemberController.cs

@@ -40,7 +40,7 @@ namespace Umbraco.Web.BackOffice.Controllers
     /// This controller is decorated with the UmbracoApplicationAuthorizeAttribute which means that any user requesting
     /// access to ALL of the methods on this controller will need access to the member application.
     /// </remarks>
-    [PluginController("UmbracoApi")]
+    [PluginController(Constants.Web.Mvc.BackOfficeApiArea)]
     [UmbracoApplicationAuthorize(Constants.Applications.Members)]
     [OutgoingNoHyphenGuidFormat]
     public class MemberController : ContentControllerBase