[Keyboard] Add System76 Launch 3

[boehs]

Description

Upstreams https://github.com/system76/qmk_firmware

Note: Errors shown while building:

⚠ system76/launch_3: Build marker "keyboard.json" not found.
☒ system76/launch_3: LAYOUT: Layout macro should not be defined within ".h" files.
gmake: Warning: File 'keyboards/system76/launch_3/halconf.h' has modification time 5572 s in the future

Types of Changes

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

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• 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.
• 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).

[drashna]

At the very least, qmk migrate will help start the process of getting this up to snuff. But most of the config in rules.mk, and a lot of the config in config.h can and should be migrated to keyboard.json (and info.json renamed to keyboard.json). Also, the 2 additional keymaps should be removed.