Expire PR previews after a week

[Eric-Arellano]

Relates to #3342.

One of the issues with our PR previews is that it takes a long time for GitHub Pages to deploy our site. We suspect this is due to how many subsites we have, each of which are fairly large. So, we want to reduce the number of sites we have, which we currently only can do by closing out PRs.

One idea is to expire old previews after 7 days. The content team signed off on this.

We would update https://github.com/Qiskit/documentation/blob/main/.github/workflows/pr-cleanup.yml to start also expiring old builds. This should be based on the deployment's metadata, rather than the PR's metadata; that is important because it's possible to restart a GH Actions job that results in a new deployment despite no new commits. TBD how to get the deployment's metadata.

[Eric-Arellano]

Let's keep this open up until we active the removal. When doing that, we may want to apply this small refactor #3432 (comment)

[Eric-Arellano]

Oh, I see now #3433 was created instead. That works. Thanks

[Eric-Arellano]

Unfortunately, our force push approach messes up things #3450. We'll want to re-implement this in a different way