Proposal: Add configobj as required dependency of astropy (instead of bundled)

[Pey Lian Lim]

The PR is at https://github.com/astropy/astropy/pull/20172 . Please comment on the PR soon before merge, especially if you object and clearly state why.

A couple of the reasons I could think of:

* if you also use configobj in your own stuff and you cannot upgrade to a compatible version (since now astropy pulls it in as a dependency)

* if you use the configobj that is bundled by astropy (you should not have but we also cannot stop you)

Thank you for your cooperation.