Add schema parameter validation to workflow

[jashapiro]

We would like to implement parameter validation as in this workflow, using the nf-schema plugin.
https://nextflow-io.github.io/nf-schema/latest/

Completing this will include creating a nextflow_schema.json file that describes the parameters for this module, and implemented the parameter validation that nf-schema allows.

If this goes well, we can use the implementation as a template for AlexsLemonade/scpca-nf#758