Initialize terrascan at runtime

[ferrarimarco]

Proposed changes

Terrascan runs initialization anyway when scanning files, so there's no point in running it at build time. Also, this works around a Terrascan bug that caused it to fail its initialization if $HOME/.terrascan directory is not present. This happens on GitHub Actions because it configures a $HOME directory that is different from ours.

Readiness checklist

In order to have this pull request merged, complete the following tasks.

Pull request author tasks

• I included all the needed documentation for this change.
• I provided the necessary tests.
• I squashed all the commits into a single commit.
• I followed the Conventional Commit v1.0.0 spec.
• I wrote the necessary upgrade instructions in the upgrade guide.
• If this pull request is about and existing issue,
  I added the Fix #ISSUE_NUMBER label to the description of the pull request.

Super-linter maintainer tasks

• Label as breaking if this change breaks compatibility with the previous released version.
• Label as either: automation, bug, documentation, enhancement, infrastructure.

[ferrarimarco]

(pushing a test only first, I want to confirm that this fails without the proposed fix that I'll push later)

[Hanse00]

Looks good. I left a comment for a clarifying question, but it's not one I think should hold up this work. Just looking to make sure I understand context.