feat: implement ras overlays

[miguelpeixe]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

Implements RAS overlays as proposed in Automattic/newspack-plugin#2708

How to test the changes in this Pull Request:

1. Checkout this branch, feat(ras): overlay management for content gate refresh newspack-plugin#2708, and add the following code to line 20 of src/view/segmentation.js:

		ras.on( 'overlay', ev => {
			console.log( ev.detail );
		} );

2. Create an overlay prompt to render for everyone and on every page view
3. Visit the front-end and open devtools
4. Wait until the prompt renders and confirm the array containing an overlay ID is logged
5. Close the prompt and confirm the overlays array is again logged and empty

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

[matticbot]

🎉 This PR is included in version 2.25.0-alpha.2 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀

[matticbot]

🎉 This PR is included in version 2.25.0 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀