feat: multiple specs in one file, with internal dependency resolution

[pmengelbert]

Take a look at test/fixtures/eraser-manager-build-dep.yml and test/fixtures/eraser-manager-runtime-dep.yml

Try building different targets.

If there is more than one spec in a spec file, you can specify the target with (for the example kubernetes-eraser-manager): --target=kubernetes-eraser-manager/mariner2/rpm or --target=kubernetes-eraser-manager-compat/mariner2/container, or similar.