Add 'extra' action

[marcosbento]

Description

Add 'extra' action, to perform custom build/test/lint/more...

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

🌦️ >> Documentation << 🌦️
https://sites.ecmwf.int/docs/dev-section/ecflow/pull-requests/PR-251

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.13%. Comparing base (d10768e) to head (2263f39).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #251      +/-   ##
===========================================
- Coverage    49.13%   49.13%   -0.01%     
===========================================
  Files         1230     1230              
  Lines        96734    96734              
  Branches     14864    14864              
===========================================
- Hits         47533    47532       -1     
- Misses       49201    49202       +1     

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