Update prometheus chart to 9.0.0

First step of updates to get us closer to the APIs to add support for Kubernetes 1.16 (which were added in the 9.3.0 version of the chart).

We need to jump to a version before due to the following:

• So 6.2.0 removed the cluster rolebinding: https://github.com/helm/charts/pull/4516
• Then 9.1.0 re-introduced one: https://github.com/helm/charts/pull/15055

So first we need to jump to a version that dropped the cluster role binding, then we need to jump to the latest version during/after a major release so we know that users got the previous change. (Logged an issue for the latter here: #1702 (closed))

I don't see any other breaking changes that impact us.

• 6.0.0 - update chart name templates, would not impact our users
• 7.0.0 - Switch from localhost to 127.0.0.1, I don't see this as breaking anything
• 8.0.0 - add optional Prometheus StatefulSets, this are disabled by default
• 9.0.0 - Support disabling the Prometheus server, also optional, still enabled by default

Part of: #1562 (closed)