Redirect Atomic wpcomstaging file paths to primary domain

### What

wpcomstaging file paths don’t redirect to the primary domain file path.

For example:
[https://awebsite.wpcomstaging.com/wp-content/uploads/2022/01/this-is-the-file.pdf]()
doesn’t redirect to
[https://awebsite.com/wp-content/uploads/2022/01/this-is-the-file.pdf]()

### Why

This significantly increase the chances of a 404's on the site, which is bad for SEO. Much like the instances found if the www. version of the domain doesn't redirect to non-www. version of the domain, or if the main wpcomstaging domain doesn't redirect to the main primary domain.

### How

Please see p1727689749025099/1727689749.025099-slack-C7YPW6K40

Start with the linked Slack discussion p1727689749025099/1727689749.025099-slack-C7YPW6K40 and reproduce the example wpcomstaging file URL. Trace the existing staging-to-primary-domain redirect behavior; done means the file path redirects from the wpcomstaging host to the corresponding primary domain path without producing a 404.

Written by the indexing model from the issue text.