EXP: Try using sphinx-autoapi instead of sphinx-automodapi

[astrofrog]

This is just an experiment in using sphinx-autoapi instead of sphinx-automodapi, to get some experience with what the differences are. For now, I'm missing the documentation of reproject.hips and reproject.mosaicking, so need to understand why that is.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.13%. Comparing base (4f8e9eb) to head (e26e47b).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #571      +/-   ##
==========================================
+ Coverage   90.12%   90.13%   +0.01%     
==========================================
  Files          30       30              
  Lines        1822     1824       +2     
==========================================
+ Hits         1642     1644       +2     
  Misses        180      180              

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