Ensure that Standard LBs have configurable number of frontend IPs

[jackfrancis]

/kind feature

Describe the solution you'd like
[A clear and concise description of what you want to happen.]

Because Kubernetes on Azure implementations share a common Standard LoadBalancer resource to route outbound traffic across all node pools, it's important to be able to scale up the number of IP addresses shared by the backend pool members for outbound access, because outbound port allocation is capped per-IP address.

This is a feature request to make sure we don't harden the Standard LoadBalancer implementation so that it is statically set to 1 public IP address for outbound SNAT. If we do so, then clusters at scale will break (port exhaustion).

This PR will do this for aks-engine, which can be used as a reference:

Azure/aks-engine#3085

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

Environment:

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

[fejta-bot]

Issues go stale after 90d of inactivity.
Mark the issue as fresh with /remove-lifecycle stale.
Stale issues rot after an additional 30d of inactivity and eventually close.

If this issue is safe to close now please do so with /close.

Send feedback to sig-testing, kubernetes/test-infra and/or fejta.
/lifecycle stale

[fejta-bot]

Stale issues rot after 30d of inactivity.
Mark the issue as fresh with /remove-lifecycle rotten.
Rotten issues close after an additional 30d of inactivity.

If this issue is safe to close now please do so with /close.

Send feedback to sig-testing, kubernetes/test-infra and/or fejta.
/lifecycle rotten

[CecileRobertMichon]

/remove-lifecycle rotten
/assign

[fejta-bot]

Issues go stale after 90d of inactivity.
Mark the issue as fresh with /remove-lifecycle stale.
Stale issues rot after an additional 30d of inactivity and eventually close.

If this issue is safe to close now please do so with /close.

Send feedback to sig-testing, kubernetes/test-infra and/or fejta.
/lifecycle stale

[CecileRobertMichon]

/remove-lifecycle stale

[CecileRobertMichon]

/help

[k8s-ci-robot]

@CecileRobertMichon:
This request has been marked as needing help from a contributor.

Please ensure the request meets the requirements listed here.

If this request no longer meets these requirements, the label can be removed
by commenting with the /remove-help command.

In response to this:

/help

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[shysank]

/assign