chore: Move modules for cross-org tests to this repository

[jvfe]

Moves all modules and subworkflows used for testing in the old test-subworkflow-remote repo to this repository, along with a schema file that should enable the feature being implemented.

[muffato]

For the record, here is what we discussed earlier today:

• Briefly expand the README to explain the purpose of the repo.
• Only keep the files that are needed for the tests and to demonstrate the feature.

[mirpedrol]

You will have to add a .nf-core.yml file with the following information:

repository_type: modules
org_path: nf-core-test

Otherwise LGTM :)

[mirpedrol]

looks good, thanks!

[jvfe]

Thanks for the review, Júlia! I don't have write access to the repository though, so I can't merge this PR.

[mirpedrol]

Merged 😄 I also changed the permissions so you can merge in the future