Select fs for sh fit metric

[geograham]

Description

Added an option to choose a flux surface with a given normalised flux, rather than the LCFS, for the spherical harmonic constraints. LCFS is still default.

Checklist

I confirm that I have completed the following checks:

• Tests run locally and pass pytest tests --reactor
• Code quality checks run locally and pass pre-commit run --from-ref develop --to-ref HEAD
• Documentation built locally and checked sphinx-build -W documentation/source documentation/build

[codecov]

Codecov Report

Attention: Patch coverage is 52.63158% with 9 lines in your changes missing coverage. Please review.

Project coverage is 76.13%. Comparing base (811471d) to head (7e1887c).
Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
...timisation/harmonics/harmonics_approx_functions.py	52.63%	9 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3642      +/-   ##
===========================================
- Coverage    76.37%   76.13%   -0.25%     
===========================================
  Files          230      230              
  Lines        26710    26763      +53     
===========================================
- Hits         20401    20375      -26     
- Misses        6309     6388      +79     

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[sonarcloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud