Ability to set a build config on the scion layer which can,

1. Clone any SCION git repository with mentioned tag, commit or branch and build SCION binaries.

scion.setBuildConfiguration({
    "mode": "build",
    "gitRepoUrl": "https://github.com/scionproto/scion.git",
    "checkout": "v0.11.0" # could be tag, branch or commit (ex "efbbd5835f33ab52389976d4b69d68fa7c087230")
})

2. Use a local directory ( absolute path ) to import the SCION binaries

scion.setBuildConfiguration({
    "mode": "release",
    "releaseLocation": "/absolute/path",   
    "version": "v0.12.0" # does nothing except suffix the directory containing the binaries
})

3. Use any HTTP URL that returns a .tar.gz file containing the binaries

scion.setBuildConfiguration({
    "mode": "release",
    "releaseLocation": "https://github.com/scionproto/scion/releases/download/v0.12.0/scion_0.12.0_amd64_linux.tar.gz"
    "version": "v0.12.0" # does nothing except suffix the directory containing the binaries
})

Things to note,
All configurations write the binaries to a directory called .scion_build_output in the current working directory.
the directory will contain sudirectories with the binaries named with a suffix to either the version or the checkout.
the build is not repeated for the same checkout or version.
any scion output will now have shared directories with docker volumes, so deleting the binaries or the shared folder will break the produced docker compose configuration.
I did not make another file for the ScionBuildConfig class since I was unsure where it could go in the project.
And I need help nailing down how changing the build config for individual nodes could look like.