ci: Add workflow to check for new UN geodata

[camdecoster]

Description

Add CI workflow to check for new UN geodata.

Changes

• Add new workflow/script for check

Testing

• Try running the workflow manually

Notes

• The first time this is run, it will create an issue requesting an update with a hidden timestamp. This can be closed.
• Subsequent runs will find the old issue and the hidden timestamp and check against that
• If the issue timestamp is older than the one from the API check, a new issue will be created. Otherwise it's a no-op.