Update zenodo to be easy to use with astropy release procedures

This issue is specifically about the core package, but it's in `astropy-project` because it probably applies to anyone else who's using Zenodo for managing DOIs, etc.

* It's a bit opaque how Zenodo decides this, but however it's done, it appears the Zenodo entry is *not* associated with the shared astropy account. That should happen automatically somehow if possible when the hook is triggered.
* Newer versions of the Astropy Zenodo entry do not appear associated with older ones from before Zenodo had the "Versions" concept. We should see if this can be post-hoc fixed, but if not we should do something to associate them, if only links in the metadata on Zenodo.