List of possible values of modules

[bambuchaAdm]

As follow up of #503 we would like to have list of possible vales that modules could be. It is standard practice to validate against human error, specially in place that are used for some kind of aggregation.

Suggested configuration

changelog:
  modules:
    - "module A"
    - B 

We won't provide any short syntax like modules: "foo" and always expect array in modules property - this should be rare case and is not worth to complicate solutions.