Add a weekly archiver run on Mondays that doesn't create a Github issue

[e-belfer]

Overview

What problem does this address?
We sometimes get archivers published shortly after our monthly archive run, and we may want a more granular update on changes in any data archive. However, we have budget for a monthly update of our archivers, so we don't necessarily want to be publishing all of our archives each week as changes occur.

What did you change in this PR?

• Add a second cron schedule that runs all our archivers every Monday at 8:21 AM UTC
• This schedule does not create a new Github archive - it's purely for informational purposes, and we can decide to create a Github issue / publish these archives on an as-needed basis, rather than having to close a Github issue each week.

Testing

How did you make sure this worked? How can a reviewer verify this?
This will require merging to main to verify that it works as cron jobs only run on main, but you can test a manual workflow run on this branch to make sure it hasn't completely broken the GHA.

To-do list

Tasks

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1. Update relevant documentation - like comments, docstrings, README, release notes, etc.
2. Review the PR yourself and call out any questions or issues you have