Use private endpoints for Azure blob store

[pbobov]

The private endpoints:

• are required for disconnected deployments without the internet access, and for
• allow to secure storage accounts by configuring the storage firewall to block all connections on the public endpoint for the storage service.

The private endpoints must be configured for blob services of:

1. the site's storage account, and
2. object store of ArcGIS Enterprise on Kubernetes.

[pbobov]

The fix:

• Creates private endpoints for blob stores of storage accounts of the site store and arcgis-enterprise-k8s organization object store.
• Changes the storage account replication type to ZRS (Zone-redundant storage).
• Disables shared access keys for the storage accounts.
• Adds "subnet_id" input variable to k8s-cluster Terraform template.
• Updates diagrams and READMEs.

This fix allows deploying ArcGIS Enterprise on Kubernetes in an AKS cluster with internal (no outbound internet access) subnets.