use towncrier to handle change log entries and update new pull request checklist

[zacharyburnett]

old checklist

Checklist

• added entry in CHANGES.rst (either in Bug Fixes or Changes to API)
• updated relevant tests
• updated relevant documentation
• updated relevant milestone(s)
• added relevant label(s)

new checklist

Tasks

• update or add relevant tests
• update relevant docstrings and / or docs/ page
• Does this PR change the public API? (if not, label with no-changelog-entry-needed)
  • write news fragment(s) in changes/: echo "changed something" > changes/<PR#>.<changetype>.rst (see below for change types)
  • run jwst regression tests with this branch installed ("git+https://github.com/<fork>/stdatamodels@<branch>")

news fragment change types...

• changes/<PR#>.feature.rst: new feature
• changes/<PR#>.bugfix.rst: fixes an issue
• changes/<PR#>.doc.rst: documentation change
• changes/<PR#>.removal.rst: deprecation or removal of public API
• changes/<PR#>.misc.rst: infrastructure or miscellaneous change

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.18%. Comparing base (84279cf) to head (9a02d67).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #326   +/-   ##
=======================================
  Coverage   66.18%   66.18%           
=======================================
  Files         100      100           
  Lines        5397     5397           
=======================================
  Hits         3572     3572           
  Misses       1825     1825           

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[braingram]

LGTM!