Add workflow to update DefaultMap automatically

[mondrake]

This workflow automates the update of the DefaultMap using the fileeye-mimemap utility and creates a pull request if changes are detected.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.68%. Comparing base (d85461d) to head (ba76537).

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #105      +/-   ##
============================================
- Coverage     97.70%   97.68%   -0.02%     
  Complexity      220      220              
============================================
  Files             9        9              
  Lines           522      519       -3     
============================================
- Hits            510      507       -3     
  Misses           12       12              

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