Enable firewall support for Databricks storage account

[jonnyry]

An Azure Databricks workspace has an associated Azure storage account in a managed resource group. Currently the "Public Network Access" attribute is set to storage firewall is set to "Enabled from all networks".

Since the storage account is in a managed resource group, it's not possible to directly change the storage firewall setting in the usual manner.

However the setting can controlled changed using default_storage_firewall_enabled on azurerm_databricks_workspace, IF the relevent prerequisites and private endpoints are in place:

https://learn.microsoft.com/en-us/azure/databricks/security/network/storage/firewall-support

Nb. This should apply to both Databricks workspaces:

1. Databricks authentication shared service
2. Databricks workspace service

[jonnyry]

cc @midodbricks