Validate YAML files

[ruflin]

All available yaml files in the packages should be validated for valid yaml to make sure packages only contain valid yaml.

An example where this would have been useful can be found here: elastic/package-registry#421

[ruflin]

If we validate all yaml files, we should also validate all json files.

[ph]

@ycombinator I think its part of the validation that you are currently enforcing?

[ycombinator]

Yes, this will ultimately be handled by the validation provided by the package-spec.

[ph]

Going to move the issue in that repository.

[mtojek]

Let me try to handle this.