Add monitoring of dandisets/ superdataset for "up to dateness"

Inspired by

- https://github.com/dandi/backups2datalad/issues/39

We should be updating the https://github.com/dandi/dandisets/ pretty much daily -- the single process shouldn't be taking too long since we are not doing data fetches there etc. So we need to configure a check which would check for the latest commit of https://github.com/dandi/dandisets/ and if it is older than e.g. 3 days -- report a fail. Requires research in how to accomplish it with upptime.