Add ceph/dashboard role (feature)

[sk4zuzu]

1. The Ceph dashboard itself can be easily enabled with such basic steps executed on mgrs (for example):

ceph config set mgr mgr/dashboard/ssl false
ceph dashboard set-pwd-policy-enabled false

ceph mgr module disable dashboard
ceph mgr module enable dashboard

ceph dashboard ac-user-create oneadmin -i- administrator <<< password

and then accessed at http://mgr-ip:8080/.

2. We can reuse Prometheus and Grafana instances we deploy already in OpenNebula. To enable Prometheus module in Ceph:

ceph mgr module enable prometheus

then Prometheus config needs to be updated like so (the Ceph exporters run on mgrs on the 9283/TCP port):

global:
  scrape_interval: 5s
scrape_configs:
  - job_name: 'prometheus'
    static_configs:
      - targets: ['localhost:9090']
  - job_name: 'ceph'
    static_configs:
      - targets: ['localhost:9283']
  - job_name: 'node-exporter'
    static_configs:
      - targets: ['localhost:9100']

3. Because we deploy our own Prometheus and Grafana instances already, there is little value in using ceph-dashboard role from ceph-ansible (which tries to install some components with docker / podman). Ideally all the above config could be implemented in a simple ceph/dashboard role in one-deploy 👍 .

☝️ 😌