TUF: Allow for TUF to be built in a way that supports Docker/Podman not just Kubernetes

[cooktheryan]

Description
Right now https://github.com/sigstore/scaffolding/blob/main/cmd/tuf/server/main.go is written to where the container can only run in Kubernetes. I think if we handle the initial steps to handle Kubernetes or some var if running in a container before the panic we could extend this image to be able to run in Podman or Docker. I believe @sabre1041 had a hack for this at some point