Update HELM references for the latest Helm release

[aimeeu]

https://spinnaker.io/guides/user/kubernetes-v2/deploy-helm/

From Chad Tripod @ Armory:
Could we put on the backlog a refresh of our HELM3 docs? In the past month I've talked with several organizations finally getting to the maturity stage with Kubernetes that they're packaging apps in HELM for their developers to input values into for each env. It will also need an equivalent chart Using Spinnaker HELM3 vs using HELM upgrade directly on the cluster as there is release capabilities for blue/green which Spinnaker likes to own.

The docs need to move to HELM3. Nobody uses HELM2 as it required tiller (an agent that ran in Kubernetes for HELM) and really was a first run at templating kubernetes configs. It should be assumed moving forward ALL orgs will use HELM3.