Multi executors for one flow

[ChrainWang]

New feature

Distribute pipeline processes to different executor

Usage scenario

I'm working on a hybird cloud project. Some process of the pipeline needs to be run on on-prem servers (which is a special hardware actually), while others can be run with AWS batch.

It's also appriciated if anybody knows existing ways to do this.

[bentsherman]

See the docs on hybrid workloads: https://nextflow.io/docs/latest/aws.html#hybrid-workloads