Add Finn to maintainers and codeowners

[mch2]

Description

Adding Finn as maintainer after maintainer vote was held.

Related Issues

N/A

Check List

• [ ] New functionality includes testing.
• [ ] New functionality has been documented.
• [ ] API changes companion pull request created.
• [ ] Commits are signed per the DCO using --signoff.
• [ ] Public documentation issue/PR created.

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