How-To: configure for on-premise cluster

Provide documentation indicating how to configure for an on-premise cluster.
This should show how to run up the container, plus then how we plug in the various cluster nodes and credentials.

The main things are basically:

• Install Couchbase server as per docs - link out, we're not documenting this
• Deploy operator - use Ansible role: https://github.com/couchbaselabs/ansible-couchbase-exporter
• Deploy CMOS - install docker/podman & run the CMOS container with defaults
• Configure CMOS for your cluster

Focus on CentOS 7 initially for 0.1 release.

We have some overnight tests that run Vagrant nodes and set everything up that can be used as a starting point: https://github.com/couchbaselabs/observability/blob/b794c1bf66c4b9fa60ac3b3f8f7afb324a6daa70/.github/workflows/cron-build.yml#L87-L127