Set start script options as environment variables for the image operaton/operaton

[javahippie]

Currently there is no easy way to pass start script arguments to the Docker container, e.g. per ENV. It is possible to pass them via overrides, but having a mechanism which can be documented and works for both Docker CLI and compose might make adaption for users easier.

An override currently looks like this:

docker run --entrypoint '/bin/sh' -p8080:8080 operaton/operaton -c './operaton.sh --webapps --rest'