[DRAFT][Terraform - AKS] Enable Azure Policy addon

[yelghali]

Azure Policy extends Gatekeeper v3, an admission controller webhook for Open Policy Agent (OPA), to apply at-scale enforcements and safeguards on your clusters in a centralized, consistent manner. Azure Policy makes it possible to manage and report on the compliance state of your Kubernetes clusters from one place. The add-on enacts the following functions:

Checks with Azure Policy service for policy assignments to the cluster.
Deploys policy definitions into the cluster as constraint template and constraint custom resources.
Reports auditing and compliance details back to Azure Policy service.

c.f https://learn.microsoft.com/en-us/azure/governance/policy/concepts/policy-for-kubernetes

code scan check
azure_policy_enabled = True