docs: reformulate the section on downloading a whole catalog

[ManonMarchand]

Hello astroquery 🙂

I think that this reformulation of the section Get a whole catalog might fix the two documentation issues #3167 and #2503

Namely:

• explicitly say that there is more information on the columns in their description (the content of the tooltips from the webpages)
• demonstrate the usefulness of row_limit

I also tried to add the idea that downloading a lot of catalogs at once (which was the first example before and now comes a bit later) is a costly operation.

What are your thoughts?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.68%. Comparing base (e447461) to head (c9f1b6d).
Report is 2 commits behind head on main.

Additional details and impacted files

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##             main    #3170   +/-   ##
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  Coverage   67.68%   67.68%           
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  Files         229      229           
  Lines       18365    18365           
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  Hits        12430    12430           
  Misses       5935     5935           

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[keflavich]

The new documentation looks great, thanks!

[bsipocz]

Thank you @ManonMarchand!

[bsipocz]

Please feel free to close the issues as you see fit, we can always reopen or do a follow-up if/when more user feedback comes in.