Adding v3 JSON for dactyl manuform 4x6

[shiroshiro14]

Description

Adding v3 JSON for Dactyl Manuform 4x6

QMK Pull Request

https://github.com/qmk/qmk_firmware/tree/master/keyboards/handwired/dactyl_manuform/4x6/keymaps

Checklist

• The VIA support for this keyboard is MERGED in QMK 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