SKIP UPDATE CHECK fix Mimir pod errors

General MR

Summary

This MR fixes some of the issues around Mimir when istio is enabled. Specifically, it:

• uses a postRenderer to set appProtocol on headless service ports so that istio properly detects their protocols and creates listeners
• disables the query scheduler entirely when istio is enabled
• configures Mimir as a prometheus data source within Grafana

Linked Issue

Works towards resolving big-bang/apps/sandbox/mimir#32

Upgrade Notices

N/A