Update documentation with Helm 3 syntax

Summary

All of our documentation currently uses exclusively Helm v2 syntax. With Helm 3, some of this syntax has changed.

We need to:

• Provide both syntaxes, until this chart supports only Helm v3
• Key changes:
  • helm install now requires name or --generate-name, inverse of before.
  • helm delete is an alias of helm uninstall (new syntax) and assumes --purge.
• Remind that stable repository is no longer included by default in Helm v3