Related to #494
This feature is mostly a built-in alternative to the `incubator/raw` chart without external dependency and has
access to helmfile's own template functions and template data.
The expected use-case of this feature is to add arbitrary K8s resources to your deployment.
Unlike the original issue raised in #494 this doesn't enable you to add arbitary resources to a release. That's another story. But this would be a good foundation for that, too.