Add extra_fields to AssetDefinition

[gadomski]

Related Issue(s):

• Closes Add extra_fields to extensions.item_assets.AssetDefinition #855

Description:

Pretty simple.

PR Checklist:

• Code is formatted (run pre-commit run --all-files)
• Tests pass (run scripts/test)
• Documentation has been updated to reflect changes, if applicable
• This PR maintains or improves overall codebase code coverage.
• Changes are added to the CHANGELOG. See the docs for information about adding to the changelog.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.32%. Comparing base (ba07305) to head (66b4a1b).
Report is 318 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1003      +/-   ##
==========================================
+ Coverage   90.15%   90.32%   +0.16%     
==========================================
  Files          47       47              
  Lines        6178     6180       +2     
  Branches      926      927       +1     
==========================================
+ Hits         5570     5582      +12     
+ Misses        426      420       -6     
+ Partials      182      178       -4     

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