Update examples to point towards example gallery

[eteq]

This is a more targeted re-hash of #140 and is a complement to astropy/astropy#7242.

Once astropy/astropy#7242 is done, we should update the examples page (http://www.astropy.org/astropy-tutorials/examples.html) to use the same "card" format as the tutorials page, but for the examples. This talks back to astropy/astropy#7242 in that we would hope that the resolution of that would provide an easy way to plug it into the javascript used in the learn site. Possibly the easiest thing there is to provide magic keywords that will then let us use the exact same thing as what we plan to do with the documentation?

[kelle]

This question was revived at the 2025 Coordination Meeting. What's our plan to use the .. example:: directive in Sphinx? Are we going to use it? Can it be removed from the docs?