Add shelfmt

[igorpecovnik]

Description

Please include a summary of the change and which issue is fixed. Provide relevant motivation and context. Ensure that no new external dependencies are introduced in this change.

Issue reference:
Related documentation:

Implementation Details

Provide a detailed description of the implementation. Include the following:

• Key changes introduced by this PR
• Justification for the changes
• Confirmation that no new external dependencies or modules have been introduced

Documentation Summary

• Metadata Included:
  Did you include the metadata (associative arrays) in the code? Ensure that metadata for modules, jobs, and runtime has been updated appropriately.

• Document Generated:
  Did you generate the updated documentation using armbian-configng --doc? Confirm if the command was run to update README.md and provide any relevant details.

Testing Procedure

Describe the tests you ran to verify your changes. Provide relevant details about your test configuration.

• Test 1: Description and results
• Test 2: Description and results

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have ensured that my changes do not introduce new warnings or errors
• No new external dependencies are included
• Changes have been tested and verified
• I have included necessary metadata in the code, including associative arrays