This seems to have gotten broken, it complains about some resources that
can't be found:

```
level=error ts=2022-09-30T08:09:08.703284478Z caller=klog.go:116 component=k8s_client_runtime func=ErrorDepth msg="status \"default/wire-server-metrics-kube-p-prometheus\" failed: failed to update status subresource: prometheuses.monitoring.coreos.com \"wire-server-metrics-kube-p-prometheus\" not found"
```

Describing how to install a monitoring system, shipping our own wrapper
chart, and documenting how to install it shouldn't be something we did
in first place. It's a potential endless game of whack-a-mole with
upstream changes, and mirroring it downstream in our documentation
shouldn't be part of wire-server.

Instead, describe what wire-server can do, how it marks its metrics
endpoints via ServiceMonitor, and refer to the upstream docs of two
commonly used metrics operators.