Filter the text_representation metadata in the contents manager

[mwouts]

Fixes #900
And also #901

[codecov]

Codecov Report

Merging #903 (cfc9e1c) into main (57d83aa) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #903      +/-   ##
==========================================
+ Coverage   99.04%   99.06%   +0.01%     
==========================================
  Files         115      116       +1     
  Lines       10721    10779      +58     
==========================================
+ Hits        10619    10678      +59     
+ Misses        102      101       -1     

Impacted Files	Coverage Δ
jupytext/cli.py	95.87% <ø> (+0.18%)	⬆️
jupytext/contentsmanager.py	97.61% <100.00%> (ø)
jupytext/jupytext.py	98.40% <100.00%> (+0.02%)	⬆️
jupytext/version.py	100.00% <100.00%> (ø)
tests/test_cm_config.py	100.00% <100.00%> (ø)
tests/test_pre_commit_1_sync_with_config.py	100.00% <100.00%> (ø)

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[lgtm-com]

This pull request introduces 1 alert when merging 1365865 into 57d83aa - view on LGTM.com

new alerts:

• 1 for Module is imported with 'import' and 'import from'