* Previous version of multiple overrides of the default value of ZMK_USB
were problematic. Move to using board _defconfig files for the
defaults for those, along with proper `depends on` for ZMK_USB that
accounts for split and split roles.
Updated existing pre-commit hooks and added some new hooks:
- Remove trailing whitespace
- Ensure every non-empty file ends with a new line
- Check YAML file validity
- Prevent adding large files
- Ensure any scripts with shebangs are executable
Added a GitHub action to run pre-commit on every commit. Removed any
existing actions which duplicate pre-commit.
Ran pre-commit on the codebase.
