docs: align API reference package name with PyPI

[vdusek]

The package name is rendered as the label on the docs website API reference pages, so this renames it back from apify-client-python-website to apify-client (the PyPI package).

@B4nan tagging you as a reviewer since you changed this recently — let me know if there was any reasoning behind it that I'm missing.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.82%. Comparing base (f72b087) to head (0b65536).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #849      +/-   ##
==========================================
+ Coverage   94.72%   94.82%   +0.09%     
==========================================
  Files          48       48              
  Lines        5045     5045              
==========================================
+ Hits         4779     4784       +5     
+ Misses        266      261       -5     

Flag	Coverage Δ
integration	93.22% <ø> (+0.39%)	⬆️
unit	83.52% <ø> (ø)

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