Add support for HA mode on standard load balancer

[feiskyer]

Is your feature request related to a problem?/Why is this needed

This is a new feature request to add support for HA mode on standard load balancer via service annotation.

Describe the solution you'd like in detail

Add a new service annotation service.beta.kubernetes.io/azure-load-balancer-enable-high-availability-mode. And when this annotation is set to true, the following configuration would be added in SLB rule:

"loadBalancingRules": [ 
         { 
           "name": "HTTPLBRule", 
           "properties": { 
             "enableHighAvailabilityMode": true, 
             ...
             }
          }   
]

Describe alternatives you've considered

Additional context

Depends on #403, the feature is only available in Azure network API version 2020-08-01.

[feiskyer]

the new property is not available in Azure Go SDK yet.

/hold

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[MartinForReal]

related #429

[MartinForReal]

Should this issue be closed? @feiskyer

[feiskyer]

this is still not supported yet.