feat(loadbalancer): floating IP addresses

[peknur]

This PR adds floating IP address support to load balancer service.

Usage
Create deployment:

$ kubectl create deployment --image=ghcr.io/upcloudltd/hello hello-uks

Create load balancer service using floating IP address 94.94.0.162:

apiVersion: v1
kind: Service
metadata:
  annotations:
    service.beta.kubernetes.io/upcloud-load-balancer-config: |
      {
          "plan": "essentials",
          "ip_addresses": [
              {
                  "address": "94.94.0.162",
                  "network_name": "public-IPv4"
              }
          ]
      }
  labels:
    app: hello-uks
  name: hello-uks
spec:
  ports:
  - port: 80
    protocol: TCP
  selector:
    app: hello-uks
  type: LoadBalancer