[AKS] fix example validation errors for new endpoints

[mboersma]

Fixes the remaining oav validate-example errors in the new stable and preview endpoints for AKS.

@zqingqing1 can you check that these changes are correct? I validated we see no warnings now with these commands:

$ cd $HOME/Projects/azure-rest-api-specs/specification/containerservices/resource-manager/Microsoft.ContainerService
$ find . -not -path "*examples/*" -not -path "*/location.json" -name "*.json" -exec oav validate-example -l warn {} \;
$ find . -not -path "*examples/*" -not -path "*/location.json" -name "*.json" -exec oav validate-spec -l warn {} \;

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[openapi-portal-comment]

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[azuresdkci]

Can one of the admins verify this patch?

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[zqingqing1]

lgtm