Add shuguet shu89 split keyboard (PCB + Case are open-source)

[shuguet]

Description

Adding on keyboard and it's associated keymap.
This is an 89 keys split keyboard, made up of a single (breakable) PCB + a case (can be either 3D printed or CNC made).
Both case and PCBs are done, only the CNC technical drawings are left TODO.

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).

[shuguet]

Thank you for the review @waffle87 , I've updated almost all asks, just waiting on more context surrounding lighting and VIA and how to make a purely config/data-driven keyboard like mine (without a rules.mk file) work with VIA, if not the way I did it here (suggested on discord)

[shuguet]

Hum?

[shu @ shu-workstation:~/code/qmk_firmware]$ qmk lint -kb shuguet/shu89
Ψ Lint check passed!
[shu @ shu-workstation:~/code/qmk_firmware]$

[shuguet]

I believe I've made all requested changes (@zvecr @drashna @waffle87 ).
If I could get an approval from y'all that would be greatly appreciated 🙏