Use private endpoints for Managed Prometheus and Azure Monitor workspace

Using private Azure Monitor Workspace endpoints for monitoring AKS cluster is required to support disconnected deployments of ArcGIS Enterprise on Kubernetes in AKS clusters. However, this makes the monitoring subsystem configuration rather complex.

I was able to configure Azure Monitor Workspace to use private endpoints for collection data from AKS cluster (see https://learn.microsoft.com/en-us/azure/azure-monitor/logs/private-link-security), but was not able to configure Managed Grafana and the AKS cluster's Monitoring/Insights to query data from the private monitor workspace query endpoints.

Connecting from managed Grafana to data source privately requires configuring "managed" private endpoints (see https://learn.microsoft.com/en-us/azure/managed-grafana/how-to-connect-to-data-source-privately). So far azurerm terraform provider does not support creating managed private endpoints for Grafana (see https://github.com/hashicorp/terraform-provider-azurerm/issues/23950). I tried creating managed private endpoints in the Azure portal, but that did not make it work anyway.

So far I don't understand how to support querying data from the private monitor workspace query endpoints in the AKS cluster's Monitoring/Insights view in the Azure portal.

> The code for private endpoint configuration for Azure Monitor Workspace is currently commented out in k8s-cluster Terraform module.