JP-4424: Use median error for imaging outlier detection

[melanieclarke]

Resolves JP-4424

WIP: draft for testing

Try using median error estimates instead of input error for thresholding imaging outliers.

Tasks

• If you have a specific reviewer in mind, tag them.
• add a build milestone, i.e. Build 12.0 (use the latest build if not sure)
• Does this PR change user-facing code / API? (if not, label with no-changelog-entry-needed)
  • write news fragment(s) in changes/: echo "changed something" > changes/<PR#>.<changetype>.rst (see changelog readme for instructions)
    • if your change breaks step-level or public API (as defined in the docs), also add a changes/<PR#>.breaking.rst news fragment
  • update or add relevant tests
  • update relevant docstrings and / or docs/ page
  • start a regression test and include a link to the running job (click here for instructions)
    • Do truth files need to be updated ("okified")?
      • after the reviewer has approved these changes, run okify_regtests to update the truth files
• if a JIRA ticket exists, make sure it is resolved properly

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.86%. Comparing base (ba79a44) to head (d330c8b).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10753      +/-   ##
==========================================
- Coverage   87.86%   87.86%   -0.01%     
==========================================
  Files         372      372              
  Lines       40364    40364              
==========================================
- Hits        35465    35464       -1     
- Misses       4899     4900       +1     

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