[AKS] managed outbound ips should be None if specifying other lb props

[tyler-lloyd]

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This addresses #4205 / Azure/azure-cli#20693 and ensures the managed outbound IP count properties are persisted if only updating count or count_ipv6.

The base class's version of configure_load_balancer_profile will overwrite count ipv6 if count is updated, therefore we need to save this value prior to calling the base class and add it back if 1) it is omitted in the current context and 2) outbound IPs and outbound IP prefixes are also omitted.

Similarly, if count_ipv6 is being updated, then the previous value of count needs to be saved and added back after the base class is called.

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[FumingZhang]

The PR looks good to me. Please also update version and history, thus we could release a new version to fix the issue.