Feature/eskip2routegroup command

[aryszka]

• [x] implement converter logic
• [x] test with Kubernetes with and without host validation
• [x] integrate the temporary command with the existing eskip supplementary tool as a subcommand
• [x] move the main logic to the dataclients/kubernetes/definitions as library function FromEskip
• [ ] documentation and usage
• [ ] release manifests (Docker and binaries)

[szuecs]

Great tool! Do you want to put the binary into the docker container? I am not sure if we should bloat the image, wdyt?

[aryszka]

we can add it. The amd64 docker image already has it. I don't think it is too much bloat, because the skipper command 37M, while the eskip is only 7.7M