ENH: Add option to keep original json structure for one input roi

[levje]

Quick description

Please include a summary of the changes and the related issue(s) or improvement(s).
Please also include relevant motivation and context. List any dependencies that are required for this change if needed.

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Type of change

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

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Checklist

• My code follows the style guidelines of this project (run autopep8)
• I added relevant citations to scripts, modules and functions docstrings and descriptions
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I moved all functions from the script file (except the argparser and main) to scilpy modules
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.59%. Comparing base (47159d4) to head (d2b3e25).
⚠️ Report is 2 commits behind head on master.

❌ Your project status has failed because the head coverage (72.59%) is below the target coverage (75.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1281   +/-   ##
=======================================
  Coverage   72.59%   72.59%           
=======================================
  Files         294      294           
  Lines       25337    25338    +1     
  Branches     3546     3546           
=======================================
+ Hits        18393    18395    +2     
+ Misses       5448     5447    -1     
  Partials     1496     1496           

Flag	Coverage Δ
smoketests	69.78% <100.00%> (+<0.01%)	⬆️
unittests	13.28% <0.00%> (-0.01%)	⬇️

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Components	Coverage Δ
Scripts	75.45% <100.00%> (+<0.01%)	⬆️
Library	69.19% <ø> (ø)

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