I2I: New extension - changes links to modals

### Summary

We are looking for a solution to:
1. get all links on a AMP website,
2. send the links URL's to our API,
3. get all links from the website matching URL's returned by our API,
4. replace default click action by opening a modal with an iframe,
5. allow closing the modal.

More details to be given after overall evaluation.

### Design Document

_No response_

### Motivation

We would like to integrate our technology with AMP.
As far as I know there is no available solution to do it right now.
Is such a solution possible with the existing components?
Is such a solution allowed to be an AMP extension?

### Alternative Solutions

We've considered:
- `amp-script` - it would require full page content to be wrapped in amp-script,
- `amp-ad` - it is semantically and functionally incorrect.

We've analyzed `amp-skimlinks`, `amp-smartlinks` and `LinkRewriter` as they provide similar solutions in terms of calling API and replacing URL's but they are third party extensions and LinkRewriter doesn't match our needs in terms of opening a modal.

### Launch Tracker

_No response_

### Notifications

/cc @ampproject/wg-approvers