[FEATURE] Add `stub` support to every module

Using command stub blocks in Nextflow is useful when developing syntax and quickly testing pipelines. However, its use within nf-core is limited because the vast majority of nf-core modules do not have stub blocks.

My suggestion is to require that every module should have a stub block. All 1095 of them :trollface:

We can lint for the presence of this in linting and also potentially run with -stub-run in the module CI.

Although adding a stub block for one or two modules is not difficult, adding it for all will be a significant effort. This could be a nice project focus for a future hackathon(s).

### Tasks