feature: update code to support Django CMS 5

[metaforx]

• Add requirement specifications for Django CMS >=5.0.0a1
• Add new test requirement files for Django CMS 5 matrix
• Update docs

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.22%. Comparing base (bf441ad) to head (a621978).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #29   +/-   ##
=======================================
  Coverage   81.22%   81.22%           
=======================================
  Files          12       12           
  Lines         474      474           
  Branches       41       41           
=======================================
  Hits          385      385           
  Misses         63       63           
  Partials       26       26           

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