Don't use experimental readthedocs build.commands config

[cosmicBboy]

This PR changes the monodocs readthedocs config so that it uses the customizeable readthedocs build steps instead of the experimental build.commands config key. This is because there are some issues with correctly rendering the readthedocs flyout menu: readthedocs/readthedocs.org#10955

Preview: https://flyte-next.readthedocs.io/en/monodocs-readthedocs-config/

vs.

https://flyte-next.readthedocs.io/en/latest/ (readthedocs inserted dropdown is missing)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (398e5cb) 59.03% compared to head (17e44b7) 59.03%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4606   +/-   ##
=======================================
  Coverage   59.03%   59.03%           
=======================================
  Files         622      622           
  Lines       52682    52682           
=======================================
+ Hits        31102    31103    +1     
+ Misses      19098    19097    -1     
  Partials     2482     2482           

Flag	Coverage Δ
unittests	59.03% <ø> (+<0.01%)	⬆️

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[cosmicBboy]

@thomasjpfan I opted for your solution to this, because readthedocs adds additional configuration to the user-supplied conf.py file, and not doing this will cause issues such as not showing the readthedocs version dropdown.