support helm plugins configuration & invocation

[poblin-orange]

Some helm repos require helm plugins

Example plugins:

• Helm release deployment utils
  • https://github.com/databus23/helm-diff: displays changes when applying helm upgrade
• Helm chart publication:
  • JCR https://github.com/belitre/helm-push-artifactory-plugin : publish helm chart to artifactory
  • S3 plugin once used by Stark&Wayne
• Test support
  • helm-unittest: https://github.com/lrills/helm-unittest
  • CT (chart testing) https://github.com/helm/chart-testing/blob/master/doc/ct.md used in percona-helm-charts not a helm plugin

[obeyler]

As workaround helm chart can be directly apply using their tgz. (in this case you don't need to add the repo)
Nota bene: I try to add s3 plugin but even with it the helm chart of Stack&Wayne wasn't loaded successfuly.

[obeyler]

s3 plugin is no more used by community