Change default auto_download to False for IERS tables #15248

Problem: Setting default to True resulted in unnecessary downloads, especially when users don't even care about time precision (e.g., using astropy to read FITS files) or from automated CI services for downstream packages. This resulted in a lot of spam to the services we pull the data from.

However, this might be controversial to people who do care about the precision because they would need to change the default now to get the old behavior back.

Alternative suggestions to solve the same problem are welcomed.

cc @mhvk @eteq @astropy/devops-maintainers @astropy/astropy-project-release-team

Might be related:

• Possible improvements to how IERS is handled #9227