annotations at the wrong place in AzureDNS example

[jonas-budde]

Manifest with wrong annotations:
https://github.com/kubernetes-sigs/external-dns/blob/master/docs/tutorials/azure.md#azure-load-balancer-option-expose-an-nginx-service-with-a-load-balancer

What happened:
I copied the example above and got an error while applying the manifest.

...strict decoding error: unknown field "annotations"

What you expected to happen:

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:

The annotations for the service should be under metadata like so:

apiVersion: v1
kind: Service
metadata:
  name: nginx-svc
  annotations:
    external-dns.alpha.kubernetes.io/hostname: server.example.com
spec:
...

Environment:

• External-DNS version (use external-dns --version):
• DNS provider:
• Others: