Fix rtd config to use extras

[willingc]

What does this PR do?

Update RTD build to configure settings to use docs extras.

Also manually enabled PR RTD builds.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.99%. Comparing base (cb2eb37) to head (e4c1755).
⚠️ Report is 33 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #836      +/-   ##
==========================================
- Coverage   91.54%   90.99%   -0.56%     
==========================================
  Files          17       17              
  Lines        1621     1632      +11     
==========================================
+ Hits         1484     1485       +1     
- Misses        137      147      +10     

see 3 files with indirect coverage changes

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