Be able to set the flat-field heuristic option via osa cfg

[morcuended]

only for calibration script

[codecov[bot]]

Codecov Report

Base: 83.17% // Head: 83.16% // Decreases project coverage by -0.01% :warning:

Coverage data is based on head (42e79e6) compared to base (8a7a7d1). Patch coverage: 57.14% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #208 +/- ## ========================================== - Coverage 83.17% 83.16% -0.02% ========================================== Files 57 57 Lines 4761 4764 +3 ========================================== + Hits 3960 3962 +2 - Misses 801 802 +1 ``` | [Impacted Files](https://codecov.io/gh/cta-observatory/lstosa/pull/208?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cta-observatory) | Coverage Δ | | |---|---|---| | [osa/scripts/calibration\_pipeline.py](https://codecov.io/gh/cta-observatory/lstosa/pull/208/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cta-observatory#diff-b3NhL3NjcmlwdHMvY2FsaWJyYXRpb25fcGlwZWxpbmUucHk=) | `72.72% <57.14%> (-0.25%)` | :arrow_down: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cta-observatory). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cta-observatory)

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