Use nf-core module `meta.yml` to validate process definition

[bentsherman]

nf-core modules have a meta.yml which includes metadata about the process inputs and outputs. For example, consider fastqc:

https://github.com/nf-core/modules/blob/master/modules/nf-core/fastqc/main.nf

https://github.com/nf-core/modules/blob/master/modules/nf-core/fastqc/meta.yml

This metadata includes type information beyond what the Nextflow syntax allows, such as type annotations for val inputs / outputs. It may be possible to facilitate type checking for existing code using this metadata.

As a first iteration, we can imitate the approach already used for the parameter schema -- if the meta.yml is present, check it against the process definition to make sure they match.

In a possible second iteration, it could be used to facilitate type checking in calling sub-workflows. But here we are still limited by the lack of type annotations for workflow takes/emits as well as some problems with operators.