Improve error classification for PublicIPAddressInUse

[dimitar-kostadinov]

How to categorize this issue?

/area ops-productivity
/kind enhancement
/platform azure

What would you like to be added:

Classify Error: Code="PublicIPAddressInUse" as User configuration issue.
If the Public IP Association for NAT Gateway is already in use the Infrastructure creation fails with:

* failed to update Public IP Association for NAT Gateway "shoot--foo--bar-nat-gateway" (Resource Group "shoot--foo--bar"): network.NatGatewaysClient#CreateOrUpdate: Failure sending request: StatusCode=400 -- Original Error: Code="PublicIPAddressInUse" Message="Resource /subscriptions/<omitted>/resourceGroups/shoot--foo--bar/providers/Microsoft.Network/natGateways/shoot--foo--bar-nat-gateway is referencing public IP address /subscriptions/<omitted>/resourceGroups/static-ip/providers/Microsoft.Network/publicIPAddresses/addr that is already allocated to resource /subscriptions/<omitted>/resourceGroups/shoot--foo--baz/providers/Microsoft.Network/natGateways/shoot--foo--baz-nat-gateway." Details=[]

Why is this needed:

Improve error classification.

[ialidzhikov]

Same as #757.