Put all files generated by sphinx into the same directory

[arcondello]

See dwavesystems/dwave-ocean-sdk#191 for an example of why this is useful

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.15%. Comparing base (fc31fd2) to head (8e0bb55).
⚠️ Report is 810 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1120   +/-   ##
=======================================
  Coverage   94.15%   94.15%           
=======================================
  Files          88       88           
  Lines        9292     9292           
=======================================
  Hits         8749     8749           
  Misses        543      543           

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