chore: optimize for best practices linter

[thomty]

Description:

This PR modifies the MAINTAINER flag deprecated by docker into the preferred LABEL system. It also moves the apt cache clear under under the apt command itself, in keeping with dockerfile optimization best practices.

Merge checklist:

• [ ] All reviewers approved
• [ ] CI build is green
• [ ] Changelog record added
• [ ] Documentation updated (not only docstrings)
• [ ] Commits are squashed

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[itsjeyd]

@thomty Thank you for your contribution!

Since there hasn't been any activity on this PR in a while I wanted to check in and see if it was still relevant?

You already got a positive review from @adzuci, so the next step towards getting this PR merged would be for you to sign the contributor agreement.

[itsjeyd]

Hi @thomty! Just a quick update that we'll be closing this PR shortly because it is stale. You may reopen this pull request, or open a new one, when you have time to come back to this work.

CC @mphilbrick211

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