Move IERS utility function that is HPC-friendly from DESI to astropy #14757

What is the problem this feature will solve?

@weaverba137: In certain environments it is necessary to avoid downloads entirely, and there are configuration items to handle that case. I've written a function that bundles all of the configuration item changes necessary to deactivate downloads and use a one-time downloaded file that can be bundled into your own package, whenever you need it, independent of the one bundled with Astropy. I suggest this can be upstreamed so that more groups can use it.

Describe the desired outcome

Re-implement https://github.com/desihub/desiutil/blob/main/py/desiutil/iers.py here in astropy.

Additional context

This came out of Astropy Coordination Meeting 2023. See #14756 (comment) for more info.