feat(service-flake): add flake for nixinit service

[seanrmurphy]

This PR adds the following:

• a flake in the service-flake directory which supports creating a package and a service.
• logic to add the package and the service to the vm image build for the qcow image type

This image gets built and booted and the service runs.

Changes are required to the service to enable it to run properly but the flake creation and adding to the image build is now working.