Add script to create test directories & files

[hacklschorsch]

Copy-pasted from https://whetstone.private.storage/privatestorage/privatestoragedesktop/-/issues/761#note_27299.

Moved from gridsync/gridsync#604.

[codecov]

Codecov Report

Merging #696 (52c19ed) into main (5ec155f) will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #696      +/-   ##
==========================================
+ Coverage   91.68%   91.70%   +0.02%     
==========================================
  Files          38       38              
  Lines        4893     4893              
  Branches      599      599              
==========================================
+ Hits         4486     4487       +1     
  Misses        278      278              
+ Partials      129      128       -1     

Flag	Coverage Δ
integration	74.04% <ø> (+0.08%)	⬆️

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Impacted Files	Coverage Δ
src/magic_folder/api_cli.py	89.72% <0.00%> (+0.39%)	⬆️

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[meejah]

If we want to keep this ad-hoc test code, it needs linting fixes and resolution of the review comment.