makefile target for helm templating charts

[jschaul]

This allows debugging helm templating issues more easily without installing everything for a quicker feedback loop. (e.g. in #1626 this would have saved some debugging time)

Checklist

• Title of this PR explains the impact of the change.
• The description provides context as to why the change should occur and what the code contributes to that effect. This could also be a link to a JIRA ticket or a Github issue, if there is one.
• The CHANGELOG.md file in the Unreleased section has been updated to explain the change which will be included in the release notes.
  • this doesn't need any mention in the changelog.

[mdimjasevic]

I tested this locally and it works.