ChoiceParam: add option to serialize overriden values

[yann-lty]

Description

This PR extends the current behavior of ChoiceParam by allowing node developers to save the list of values if they have been overridden at runtime.

Features list

• ChoiceParam: support for serialization of overridden list of possible values.

Implementation remarks

Introduce a new saveValuesOverride parameter on desc.ChoiceParam to define whether to serialize the list of possible values if they have been overridden at runtime.
If that is set to True, the ChoiceParam instance is serialized as a dictionary containing both the value and list of possible values.

[codecov]

Codecov Report

Attention: Patch coverage is 99.13043% with 1 line in your changes missing coverage. Please review.

Project coverage is 73.22%. Comparing base (8ee7b50) to head (062bc3c).
Report is 13 commits behind head on develop.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
meshroom/core/attribute.py	94.11%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2682      +/-   ##
===========================================
+ Coverage    72.79%   73.22%   +0.43%     
===========================================
  Files          129      130       +1     
  Lines         7753     7863     +110     
===========================================
+ Hits          5644     5758     +114     
+ Misses        2109     2105       -4     

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