job type `docker-image` to support custom `entrypoint`

[epDHowwD]

Is your feature request related to a problem? Please describe.
I'd like to set a custom entrypoint for job-type docker-image.

Describe the solution you'd like

{
    "version": 1,
    "jobs": [{
        "type": "docker-image",
        "name": "test",
        "image": "some-advanced-dockerimage-with-defined-entrypoint",
        "entrypoint": ["/infrabox/context/infrabox/test/entrypoint.sh"],
        "command": ["echo", "hello world"],
        "resources": { "limits": { "cpu": 1, "memory": 1024 } }
    }]
}

Workaround
Define a Dockerfile for job-type docker instead:

FROM some-advanced-dockerimage-with-defined-entrypoint
ENTRYPOINT ["/infrabox/context/infrabox/test/entrypoint.sh"]
CMD  ["echo", "hello world"]