Hide private methods in API documentation

[danielhollas]

I noticed that the current API documentation is extremely messy, because it includes all the private methods. I am not sure what was the original motivation for this, but I'd suggest to remove it.

New version:
https://aiidalab-widgets-base--606.org.readthedocs.build/en/606/apidoc/aiidalab_widgets_base.html

Additional changes:

• simplified the sphinx-apidoc invocation
• basic pins for docs dependencies to make the build more future-proof

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.21%. Comparing base (7c9a3ef) to head (86146db).
Report is 19 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #607   +/-   ##
=======================================
  Coverage   96.21%   96.21%           
=======================================
  Files          11       11           
  Lines        1188     1188           
=======================================
  Hits         1143     1143           
  Misses         45       45           

Flag	Coverage Δ
python-3.10	96.21% <ø> (ø)
python-3.9	96.21% <ø> (ø)

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[unkcpz]

@danielhollas thanks! all good.