Helm: Support for Chart.yaml fragments

[manusa]

As a user I would like to provide a fragment for my JKube-generated Chart.yaml file. The contents of this fragment file should be merged with the final Chart.yaml after it has been generated, overriding any matching values.

Similar to #2112

Relates to:

• feat: add support for kustomize api v1beta1 (#4929) fabric8io/kubernetes-client#4930
  Some of the types that were added in scope of this PR could be used for this purpose.
• Enhancement: add support to package my already existing Helm Chart  #865

[rohanKanojia]

I couldn't find a direct mapping of Chart.yaml object in Kustomize model.

However, I was able to find a struct in helm repository : Metadata.go