GHA to check common files and potentially update them

[etiennebacher]

We want to centralize documents like CoC here but don't want to propagate them by hand. Set up a GHA to check once a week whether these docs are up to date and pull them otherwise.

[willgearty]

Sounds like a good plan to me

[etiennebacher]

The infrastructure to connect resources to website is now done and works (there's a CI error in the website repo for now but that's unrelated). I'm leaving this open to remind myself to change the URL in the workflows to point to palaeoverse-quarto once the website transition is done.

Edit: the infrastructure is a bit different from what I originally wrote. Instead of periodically checking from the website repo if any documents changed here, we send a notification to the website repo from here when something changed. This notification then triggers another workflow on the website repo to rebuild the website if necessary.