feat(atreus): original Atreus 42 keys keyboard definition

[zenlor]

Description

Adds the json definition for the original Technomancy's Atreus keyboard.

Tested on an original PCB produced by Technomancy and a FalbaTech handwired.

QMK Pull Request

This is not a new keyboard, but VIA support can be built using the usual VIA_ENABLE = yes flag. eg.: my qmk_userspace

VIA Keymap Pull Request

Commit: the-via/qmk_userspace_via@a9ed5ec

Checklist

• The VIA support for this keyboard is MERGED in QMK master already (MANDATORY)
• VIA keymap is MERGED in VIA userspace master already (MANDATORY)
• The VIA definition follows the guide here: https://caniusevia.com/docs/layouts
• I have a V3 JSON version for this keyboard definition.(MANDATORY)
• I have formatted the JSON file to have consistent formatting with the rest of the repository.
• I have tested this keyboard definition using VIA's "Design" tab.
• I have tested this keyboard definition with firmware on a device.
• I have assigned alpha keys and modifier keys with the correct colors.
• The Vendor ID is not 0xFEED