BUG: fix broken links in documentation

There has been quite a few problematic links, some of them are genuinely broken, others may have been just redirected (ideally we need to then update in the docs), etc.

https://github.com/astropy/astroquery/actions/runs/4176953967/jobs/7233911999

Start with the linked GitHub Actions run to identify the reported documentation link failures. Review the affected documentation links, distinguish broken links from redirects, update the documentation where appropriate, and verify that the link checks pass.

Written by the indexing model from the issue text.