PyPI organization: astropy

We got https://pypi.org/org/astropy/ (https://docs.pypi.org/organization-accounts/). Need to:

* Sort out PyPI permission scheme.
* Sort out who needs what permission.
* Make sure they have 2FA.
* Transfer repos over:
* `astropy`
* Coordinated packages
* Infrastructure packages that we maintain
* Make teams for the projects, and assign team for each project as appropriate. During this process, individual access might be terminated if we decide to exclusively switch to team-based permission.
* Document this somewhere
* Put org admin under release managers role.
* #148

Start with the PyPI organization-accounts documentation and issue #148, then inventory the listed Astropy and coordinated packages. Define the permission scheme, required 2FA, repository transfers, team assignments, and release-manager documentation; the work is done when these decisions are recorded and access is aligned.

Written by the indexing model from the issue text.