Simple Aperture Photometry Plugin: Auto-populate background

[pllim]

Description

This pull request is to implement the most minimal version of background auto-population as proposed at #1050 (comment) .

Fixes #1050

TODO

• Is there some nicer way to control the GUI behavior? Maybe @kecnry knows. He mentioned observe.
• Add tests.
• Add change log.

Checklist for package maintainer(s)

This checklist is meant to remind the package maintainer(s) who will review this pull request of some common things to look for. This list is not exhaustive.

• Are two approvals required? Branch protection rule does not check for the second approval. If a second approval is not necessary, please apply the trivial label.
• Do the proposed changes actually accomplish desired goals? Also manually run the affected example notebooks, if necessary.
• Do the proposed changes follow the STScI Style Guides?
• Are tests added/updated as required? If so, do they follow the STScI Style Guides?
• Are docs added/updated as required? If so, do they follow the STScI Style Guides?
• Did the CI pass? If not, are the failures related?
• Is a change log needed? If yes, is it added to CHANGES.rst?
• Is a milestone set? Milestone is only currently required for PRs related to Imviz MVP.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[codecov]

Codecov Report

Merging #1109 (e9c3227) into main (074d51d) will increase coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1109      +/-   ##
==========================================
+ Coverage   76.37%   76.46%   +0.08%     
==========================================
  Files          82       82              
  Lines        6425     6449      +24     
==========================================
+ Hits         4907     4931      +24     
  Misses       1518     1518              

Impacted Files	Coverage Δ
...imviz/plugins/aper_phot_simple/aper_phot_simple.py	95.14% <100.00%> (+0.52%)	⬆️

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[ibusko]

This works as expected.

[rosteen]

Looks good to me, the generated background values seem sensible based on the regions I was selecting to test.