Add annotation to specify DHCP lease hostname

[shkuviak]

Following my previous issue #614 , i made little changes to be able to specify hostname sent to dhcp server when requesting lease using an annotation as the following:

apiVersion: v1
kind: Service
metadata:
  name: nginx-dhcp
  annotations:
    kube-vip.io/loadbalancerHostname: mydhcp-test
spec:
  loadBalancerIP: 0.0.0.0
  ports:
  - name: http
    port: 80
    protocol: TCP
    targetPort: 80
  selector:
    app: hello-world
  type: LoadBalancer

This makes DHCP aware of the hostname and makes the service accessible though local hostname resolution:

curl mydhcp-test.lan

[thebsdbox]

Nice!

[thebsdbox]

/LGTM

This is great, thanks!