when no extensions are available `pack builder inspect` should show `extensions none`

[jjbustamante]

Summary

During the developing of the issue #1486 we agreed on now showing anything related to extensions when the are not present. We don't want to affect the user experience, it could be somebody out there that is parsing the output of the inspect command.

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Reproduction

Steps

1. Make sure you have access to a builder without extensions.
2. Run the command pack builder inspect <builder-image>
3. The output result will contain all the expected information but it will also include a section like:

Extensions:
  (none)

Current behavior

Based on this PR the output template was modified to include:

Extensions:
  (none)

When no extensions are found

Expected behavior

When there are no extensions, we don't want to show anything related to extensions in the output

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Environment

pack info

This feature hasn't released yet, it is shown if the latest version of the main branch is built.

docker info

NA

[itsdarshankumar]

pls assign @jjbustamante

[itsdarshankumar]

Mistakenly unassigned @natalieparellano from notification, apologies, pls reassign