Switch from nbsphinx to myst-nb

[adamgayoso]

This works but it missing the notebook gallery thumbnails as well as myst-nb does not currently have a prolog feature where we can inject the colab links.

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (74e9890) 89.13% compared to head (e458270) 89.13%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1673   +/-   ##
=======================================
  Coverage   89.13%   89.13%           
=======================================
  Files         142      142           
  Lines       11102    11102           
=======================================
  Hits         9896     9896           
  Misses       1206     1206           

Flag	Coverage Δ
unittests	89.13% <ø> (ø)

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[adamgayoso]

@martinkim0 we can get this in but not backport it to 0.20.x, so it would come out at the next major release