JP-2546: updates and fixes for wfss_contam step

[emolter]

Resolves JP-2546

Closes #7288

This PR addresses several of the remaining tasks needed to make the wfss_contam step fully functional. Submitting a draft now so everyone can see the proposed changes, although there are still several outstanding issues. See the JIRA ticket for many more details.

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

[codecov]

Codecov Report

Attention: Patch coverage is 79.92278% with 52 lines in your changes are missing coverage. Please review.

Project coverage is 75.72%. Comparing base (6580914) to head (632fdec).
Report is 4 commits behind head on master.

❗ Current head 632fdec differs from pull request most recent head 5efdbb6. Consider uploading reports for the commit 5efdbb6 to get more accurate results

Files	Patch %	Lines
jwst/wfss_contam/wfss_contam.py	68.46%	41 Missing ⚠️
jwst/wfss_contam/observations.py	91.57%	8 Missing ⚠️
jwst/wfss_contam/wfss_contam_step.py	25.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #8417       +/-   ##
===========================================
+ Coverage   56.38%   75.72%   +19.34%     
===========================================
  Files         387      476       +89     
  Lines       38716    39661      +945     
===========================================
+ Hits        21830    30035     +8205     
+ Misses      16886     9626     -7260     

Flag	Coverage Δ		*Carryforward flag
nightly	77.74% <ø> (?)		Carriedforward from 1859827

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