.github: delete-stale-from-cloudsmith: Add job

[gastmaier]

PR Description

Adds cron job to clean-up stale artifacts on cloudsmith. Is considered a stale artifact if is from a closed pull request older than X days, and from a branch older than Y days. For branches is set to 0 ("never").

The branch case is the reason for this being a draft: by date on branch is terrible.
I though about:

• having a min value for branch, e.g., 3 years.
• distributed removal: before X time, keep only 5 commit per month, Y 1 commit per month

Still, be can consider these intermediary artifacts, were we only preserve on the 'used for' end, e.g. kuiper images, and let these be deleted.

PR Type

• Bug fix (a change that fixes an issue)
• New feature (a change that adds new functionality)
• Breaking change (a change that affects other repos or cause CIs to fail)

PR Checklist

• I have conducted a self-review of my own code changes
• I have compiled my changes, including the documentation
• I have tested the changes on the relevant hardware
• I have updated the documentation outside this repo accordingly
• I have provided links for the relevant upstream lore