Outbound LB not being set when upgrading v1alpha3 private clusters

[shysank]

/kind bug

What steps did you take and what happened:

1. install v1alpha3 providers.
2. create a private cluster. This will also create a control plane and node outbound lbs.
3. Upgrade to v1beta1.
4. change k8s version (this could be anything)
5. kcp rollout of new machine fails

What did you expect to happen:

Upgrade should be successful

Anything else you would like to add:

Reason for failure:
New machines created by kcp are not able to connect to image registry during cloud init because -> they are not added to backend pool of outbound lb becuase -> the code doesn't reach the conversion logic to set default outbound lb for v1alpha3 clusters because -> data annotation for v1alpha3 clusters is not present, and it returns here

Environment:

• cluster-api-provider-azure version:
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):

[shysank]

/priority critical-urgent

[shysank]

cc @CecileRobertMichon