feat: add extra_user_agents to BaseVOQuery

[ManonMarchand]

This PR fixes #3507

Might not be the best way to do it, I was a bit unsure.

There will be a following PR documenting its use in the SimbadClass but I thought that it would be best to separate these changes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.40%. Comparing base (e1aa370) to head (ca66a07).
⚠️ Report is 185 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3526   +/-   ##
=======================================
  Coverage   72.39%   72.40%           
=======================================
  Files         219      219           
  Lines       20432    20436    +4     
=======================================
+ Hits        14792    14796    +4     
  Misses       5640     5640           

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[bsipocz]

This looks all good, thanks!

(I'm not sure if you've seen, but Markus also changed the user agent in pyvo; though of course that is not yet usable for astroquery purposes (will be released in pyvo 1.9 and it will take some time for that version to be the minimum requirement)

[ManonMarchand]

Thanks for the merge!

I've seen Markus's changes and his suggestions for a standard user agent that'd tell VO services that the current user is doing actual science. We all have huge load issues these days, this might help? 🤞