added zmk firmware configs

[ellahin]

Added configs for a basic numpad using ZMK firmware and moved QMK firmware to its own folder.

[mattdibi]

Hi there @ellahin,

thank you for your contribution! Unfortunately I'm not sure it fits the goal of the current Yampad repo.

1. ZMK firmware doesn't support ATmega32U4-based MCUs (see https://zmk.dev/docs/hardware#pro_micro) Current HW assembly instruction and BOM only mention ATmega32U4 controllers
2. You contributed the Github Action responsible for building the firmware but it won't work given that it's in the wrong path (see: https://docs.github.com/en/actions/get-started/quickstart#creating-your-first-workflow)

I think a better fit for your work would be to contribute it as a new shield for ZMK (see https://zmk.dev/docs/development/hardware-integration/new-shield) with the additional build instructions and updated BOM to support ZMK