Support multiple Nextflow versions

[matrulda]

Currently, a single Nextflow version is used globally. This should be extended to allow each pipeline/service to specify and use its own compatible Nextflow version.

[Aratz]

This should already be possible with NXF_VER, no? https://docs.seqera.io/nextflow/updating-nextflow#version-selection

[matrulda]

Yes, exactly, we just need to make sure that multiple versions are available offline 👍