DOC: Move sphinx-gallery examples out of core (this) repository

[pllim]

Motivation: These examples have not been updated nor expanded for a very long time. We have Learn Astropy for these sorts of tutorials. Removing these would free us from sphinx-gallery and speed up doc build (xref #16161).

Cons: Would be impossible to test these examples in PRs (using the RTD job). (Though some people see this as "pros" instead because they do not want the overhead.)

• Would supersede Transform the current example gallery into a more docs-integrated example list #7242
• Would close [3.1] Remote access when building documentation #8311

At the 2024-03-07 dev telecon, there was an idea to move these examples to their own repo(?) and only build them against stable astropy (maybe via a cron job or as part of the release process).

[mhvk]

I like the idea of moving the examples out - but having some way that we are sure to test them on cron or before a new release.

[saimn]

I don't know for the coordinates ones, but for the io examples which are mostly io.fits, most of the examples are already in the docs. Would not be too difficult to integrate the missing ones.
Arguably it's a bit more difficult to find how to do basic things in the docs since examples there are a bit everywhere. Maybe the should a Quickstart/How to do basic things page with the most common examples.

[pllim]

@saimn , there is already an extensive "Getting Started" section. Won't adding a similarly named "Quick Start" be confusing?

https://docs.astropy.org/en/latest/io/fits/index.html#getting-started

[saimn]

@pllim - Right, and most examples are already there. The one that is missing in the docs is https://docs.astropy.org/en/latest/generated/examples/io/skip_create-large-fits.html#sphx-glr-generated-examples-io-skip-create-large-fits-py but this should probably go somewhere more hidden, maybe in the FAQ. It's not really an example for newcomers :)

[pllim]

@saimn , turns out the FITS landing page link to most of them, except one. How does #16194 look?

[pllim]

Simon and I tackled io in #16194 . When I have time (read: procrastinate), I will go for coordinates! 🔥