Update adb-external-hive-metastore to use azurerm v4

[r3stl355]

One of several updates to existing templates to make them compatible with azurerm v4, tracked in https://github.com/databricks/terraform-databricks-examples/issues/144

Changes:

• Add subscription_id parameter: it is mandatory in azurerm v4
• Remove no_public_ip: it is true by default in azurerm v4
• Add terraform.tfvars file
• Update output variables
• Update README.md

Deployment was fully tested