Update CAPI quick start for CAPZ 1.16

/kind documentation

The docs at https://cluster-api.sigs.k8s.io/user/quick-start.html show steps related to Service Principals which will not work as-is with the upcoming CAPZ 1.16 because of the new default to use Workload Identity (#4765). We should update the docs to either refer to steps to set up Workload Identity or with steps to modify the AzureClusterIdentity to use Service Principal.