Add support to create a folder when selecting a new microflow/page.

When using the "Call microflow" or "Show page" action, you can choose to select a flow or page or to create a new one.

Creating a new one directly works fine, but afterwards I often have to create a folder and move the flow or page to organize the project.

I would be nice if I could directly create a folder from the selection window. Maybe a "New folder" next to the "New" button.