Changing default footprint_edge_threshold value

[astronomerritt]

Fixes #1038.

• Changed the default footprint_edge_threshold value in all configuration files packaged within Sorcha to 2.0arcsec, which is equivalent to the 10px value we got from DM.
• Minor edits to the text of the config files.
• Adjusted unit test.
• Regenerated goldens.

Review Checklist for Source Code Changes

• Does pip install still work?
• Have you written a unit test for any new functions?
• Do all the units tests run successfully?
• Does Sorcha run successfully on a test set of input files/databases?
• Have you used black on the files you have updated to confirm python programming style guide enforcement?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.11%. Comparing base (bbece40) to head (533df63).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1039      +/-   ##
==========================================
- Coverage   81.14%   81.11%   -0.04%     
==========================================
  Files          70       70              
  Lines        3166     3166              
==========================================
- Hits         2569     2568       -1     
- Misses        597      598       +1     

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