Strict syntax

[ewels]

We should start enforcing Nextflow strict syntax everywhere. Both for Nextflow language updates, and also so that the VSCode Nextflow extension doesn't throw any errors.

We can use a CI job with nextflow lint to enforce this and check for errors during material development.

• nextflow lint CI job: Add Nextflow lint GitHub Actions workflow #739
• hello_nextflow - Hello nextflow: New workflow inputs + outputs + strict syntax #743
• hello_nf-core
• nextflow_run
• nf4_science
• side_quests
• training_collections
• other