JP_3100 move straylight before flat fielding

[jemorrison]

Resolves JP-3100

This PR moves the MIRI MRS straylight step before flat fielding in the calwebb_spec2 pipeline.

Checklist for maintainers

• added entry in CHANGES.rst within the relevant release section
• updated or added relevant tests
• updated relevant documentation
• added relevant milestone
• added relevant label(s)
• ran regression tests, post a link to the Jenkins job below.
  How to run regression tests on a PR
• Make sure the JIRA ticket is resolved properly

[jemorrison]

This change was made in calwebb_spec2 in the module _process_common.
Only MRS IFU data has the straylight step and MRS data is processed in the module.

BTY - the straylight step is called other places in the code - which does not make sense to me because it is only an
MRS step. For example _process_grism and _process_niriss_soss. But I guess it does not matter because in these cases it will just get skipped - so no harm done.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +0.01 🎉

Comparison is base (aa1564e) 77.59% compared to head (6bab8a1) 77.61%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7486      +/-   ##
==========================================
+ Coverage   77.59%   77.61%   +0.01%     
==========================================
  Files         452      452              
  Lines       36091    36048      -43     
==========================================
- Hits        28005    27978      -27     
+ Misses       8086     8070      -16     

Flag	Coverage Δ		*Carryforward flag
nightly	77.60% <ø> (-0.01%)	⬇️	Carriedforward from aa1564e
unit	49.56% <0.00%> (-0.02%)	⬇️

*This pull request uses carry forward flags. Click here to find out more.

Impacted Files	Coverage Δ
jwst/pipeline/calwebb_spec2.py	93.93% <0.00%> (-0.38%)	⬇️

... and 24 files with indirect coverage changes

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[hbushouse]

LGTM.

[drlaw1558]

Looks fine to me too.

[hbushouse]

Regression test started at https://plwishmaster.stsci.edu:8081/job/RT/job/JWST-Developers-Pull-Requests/595/

[hbushouse]

Regtest results look fine. Only expected differences due to S_STRAY keyword now showing up in flat_field step outputs, because the step has now been run before flat_field.