Update Helmfile project to use Helm OCI full feature

[scottrigby]

Hi again 👋

Helm OCI is now a full feature! See our blog post on this https://helm.sh/blog/storing-charts-in-oci/. This means it's both out of experimental and more robust support has been added, tests pass, and is now considered stable.

• [ ] Update Helmfile Dockerfile to a version of Helm >= v3.8.0 (most recent would be 3.8.1) https://github.com/roboll/helmfile/blob/185bc829926911ed5bd08922ad7596658cf9164e/Dockerfile.helm3#L14
• [ ] Stop passing HELM_EXPERIMENTAL_OCI=1 to helm binary

[yxxhero]

@scottrigby agree!

[koslowdavida]

@scottrigby seconded