[New WfMS] Add support for NextFlow

[jan-janssen]

Based on the CWL support it should also be possible to add support for NextFlow:
https://www.nextflow.io/example1.html

There is even a compatibility utility which was designed to convert CWL scripts to NextFlow, unfortunately is is no longer being developed:
https://github.com/nextflow-io/cwl2nxf