Update format with format options in the notebook metadata (md:myst and md:pandoc)

[mwouts]

May fix #757

[codecov]

Codecov Report

Merging #758 (3d75792) into master (0a8b180) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #758   +/-   ##
=======================================
  Coverage   99.10%   99.10%           
=======================================
  Files         106      106           
  Lines       10012    10032   +20     
=======================================
+ Hits         9922     9942   +20     
  Misses         90       90           

Impacted Files	Coverage Δ
jupytext/jupytext.py	98.38% <100.00%> (+0.01%)	⬆️
jupytext/version.py	100.00% <100.00%> (ø)
tests/test_metadata_filter.py	100.00% <100.00%> (ø)
jupytext/config.py	96.73% <0.00%> (-0.55%)	⬇️
jupytext/metadata_filter.py	100.00% <0.00%> (+0.86%)	⬆️

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