Make ZMK builder easily upgradeable

[panzerstadt]

Updating the cached version of zmk the builder uses to the latest version, we can sort the zmk version just need some guidance on how to tell the builder to use a new version

How To Build:

• refer to README.md

ZMK upgrade Steps:

• update dockerfile base image. its currently on zmkfirmware/zmk-build-arm:stable
• build

Adding boards:

• add zmk config repo into board-config directory
• add the directory into mapper.js
• build

[panzerstadt]

tasks: basically about prepping docs, and maybe cli helpers/package json commands