PMFR4PLTFND-1316: add rbac_aad_azure_rbac_enabled var

[ajeffowens]

Ran two tests. One with rbac_aad_azure_rbac_enabled set to true, which produced an aks cluster with:

Authentication and Authorization
Microsoft Entra ID authentication with Azure RBAC

and another with the variable omitted entirely, which produced an aks cluster with:

Authentication and Authorization
Microsoft Entra ID authentication with Kubernetes RBAC

which is consistent with current default behavior

[riragh]

Few comments about this PR:

• Starting Kubernetes v1.26, the azure auth provider was removed from the kubectl binary, so user would need an alternative method to be able to authenticate to AKS. With Azure RBAC enabled, for non-interactive seamless authentication (which also helps DAC) we would need to use kubelogin. I don't see any code around that.
• We would need some documentation on how to authenticate as using the kubeconfig generated by IAC will return error.
• Additionally, if my memory serves me well, we need to disable local_accounts when using Azure RBAC.