Support for Helm 3

[srueg]

Describe the bug/feature Are there any plans for supporting Helm 3 for rendering charts?

I could imagine to support both versions by introducing a new input type helm3 for example. Fully switching to Helm 3 might have some compatibility issues as well. For example charts which use the deprecated crd-install hook won't render correctly with Helm 3.

Additional context Some Helm charts will only work correctly when rendered with Helm version 3. For example whenever CRDs are included in the new crds folder they won't be picked up by Helm 2. For example the Crossplane chart won't render correctly (CRDs missing) due to this.

[srueg]

Thinking of it again I guess it should be ok to just replace Helm 2 with 3. Since Helm 2 is being deprecated anyway: https://helm.sh/blog/helm-v2-deprecation-timeline/. And most charts work well with Helm 3.

I started a WIP PR for the upgrade: #648. There's quite a lot of changes in the library and how the template rendering works...