Check and create v6 migration directory if not exists

[DL6ER]

What does this implement/fix?

Check and create v6 migration directory before trying to move/write files there. This involves config migrations but also Teleporter importing

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Related issue or feature (if applicable): pi-hole/pi-hole#5766

Pull request in docs with documentation (if applicable): N/A

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4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)

Checklist:

• The code change is tested and works locally.
• I based my code and PRs against the repositories developmental branch.
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