Add support for Smart 68 keyboard

[Shados]

Description

Adds support for the Smart 68. Some notes:

• I based the layout off of the default used for it in its original TMK firmware, and enabled Command in it for feature-parity with that.
• Bootmagic key is also set to the one used in its original firmware.

Also, it's not entirely clear to me what "keyboard maintainer" implies in this context. Should I be putting myself there, as I have done, or should I just put qmk?

Types of Changes

• [ ] Core
• [ ] Bugfix
• [ ] New feature
• [ ] Enhancement/optimization
• [x] Keyboard (addition or update)
• [x] Keymap/layout/userspace (addition or update)
• [ ] Documentation

Checklist

• [x] My code follows the code style of this project: C, Python
• [x] I have read the PR Checklist document and have made the appropriate changes.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [ ] I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[github-actions[bot]]

Thank you for your contribution! This pull request has been automatically marked as stale because it has not had activity in the last 45 days. It will be closed in 30 days if no further activity occurs. Please feel free to give a status update now, or re-open when it's ready. For maintainers: Please label with bug, awaiting review, breaking_change, in progress, or on hold to prevent the issue from being re-flagged.

[Shados]

Not stale...