This PR adds an option to the page list dropdown that allows you to export the page as a json file, in the same format that core allows to export reusable blocks.
This will make it much easier for page template creators to save them as files we can use.

How to test

0. Pick any of your sites, go to your pages list
   1.In any of the pages, click on the ellipsis menu and then ‘export’
1. You should get a json file with this format:

{
			__file: 'wp_template',
			language: 'en',
			title: page.title,
			content: page.content,
		}