Features
- Warn when adding and enabling a systemd unit and there is no "Install"
section in the unit contents
- Add highlights to reports generated by "Validate" functions on config
structs
Changes
- Move a helper validation function to the "config/validate" package
- Move unit validation helpers to "config/shared/validations"
- Add common error types to "config/shared/errors", refactor "config/v*" to
use these errors