Add new options disableOutboundSNAT for standard load balancer

[feiskyer]

Refer kubernetes/kubernetes#75282, cloud provider adds disableOutboundSNAT when standard load balancer is configured.

Azure outbound rules are not taking effect when used together with standard load balancer .
This PR adds a new configuration for disabling SNAT for load balancer rules, so that outbound rules would be used as the egress IPs.
In such case, disableOutboundSNAT should be set to true and loadBalancerSku should be set to standard.

Supported Kubernetes versions are v1.11.9+, v1.12.7+, v1.13.5+ and v1.14.0.

@jackfrancis

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This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[jackfrancis]

keep open

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.