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 49.25%. Comparing base (64ea30d) to head (010d17d).
⚠️ Report is 15 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #251   +/-   ##
========================================
  Coverage    49.24%   49.25%           
========================================
  Files         1231     1231           
  Lines        96996    96996           
  Branches     14860    14860           
========================================
+ Hits         47767    47776    +9     
+ Misses       49229    49220    -9     

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