Component: openstack-cloud-controller-manager (occm)

FEATURE REQUEST?:

/kind feature

As a Kubernetes + occm user I would like to be able to create Prometheus endpoint (a listener with a special protocol "PROMETHEUS") so that I can easily monitor my Octavia Load Balancers using Prometheus.

What happened:
Currently the only way to do so is to use Openstack CLI / APIs
openstack loadbalancer listener create --name stats-listener --protocol PROMETHEUS --protocol-port 9100 --allowed-cidr 10.0.0.0/8 $os_octavia_id

What you expected to happen:
Create the Prometheus endpoint using annotations at Loadbalancer creation (Kubernetes service type LoadBalancer)

Annotations that we suggest to add:

kind: Service
metadata:
  name: octavia-metrics
  annotations:
    loadbalancer.openstack.org/metrics-enable: "true"
    loadbalancer.openstack.org/metrics-port: "9100"
    loadbalancer.openstack.org/metrics-allow-cidrs: "10.0.0.0/8, fe80::/10"
    loadbalancer.openstack.org/vip-address: "10.4.2.3" #  Auto-computed field based on Octavia VIP as it is required for Prometheus configuration or any other solution (currently it is not possible to retrieve private IP of public LBs) 
  labels:
    app: test-octavia
spec:
  ports:
  - name: client
    port: 80
    protocol: TCP
    targetPort: 80
  selector:
    app: nginx
  type: LoadBalancer 

Anything else we need to know?:
Related Octavia documentation:
https://docs.openstack.org/octavia/latest/user/guides/monitoring.html#monitoring-with-prometheus

As an Openstack Public Cloud Provider we are currently working on a custom CCM implementation, for this reason we can potentially do the PR associated with this request, but we'd like to at least validate the implementation before starting developments.