Allow namespace scaffold views to default to scaffold namespace templates instead of non namespace views. Fixes #15239

[codeconsole]

When

grails:
      scaffolding:
          enableNamespaceViewDefaults: true 

is enabled, namespace scaffold templates will take priority over non-namespace views.

For Example:

@Scaffold(RestfulServiceController<Event>)
class EventController {
    static namespace = 'admin'
}

@Scaffold(RestfulServiceController<Event>)
class EventController {
}

grails-app/
    views/
        event/
            index.gsp
src/main/templates/scaffolding/admin/
    index.gsp

The current behavior is /admin/event/index resolves grails-app/views/event/index.gsp

With this fix, when enableNamespaceViewDefaults is enabled, /admin/event/index will resolve src/main/templates/scaffolding/admin/index.gsp if grails-app/views/admin/event/index.gsp does not exist.

[jdaugherty]

Let's add tests & documentation to merge this.

[jdaugherty]

@codeconsole I assume this is ready to merge? @matrei once you approve, I think we can merge.

[matrei]

The current behavior is /admin/person/index resolves grails-app/views/event/index.gsp

Is this supposed to say:
The current behavior is /admin/event/index resolves grails-app/views/event/index.gsp

[codeconsole]

Is this supposed to say: The current behavior is /admin/event/index resolves grails-app/views/event/index.gsp

@matrei yes, updated