Ensure managed virtual networks are in use for Azure Synapse Workspace

Azure Synapse Workspace don't use managed virtual networks, this may make infrastructure security complex to manage.

The workspace network configuration cannot be changed after it is created; new resource must be created to enable the managed virtual network function. To do so, follow the steps below.

In Azure Console -

1. Open the Azure Portal and go to Synapse Analytics.
2. Create a new workspace.
3. On the Network tab, set Managed virtual network to Enabled.
4. Configure the rest as needed.

In Terraform -

1. In the azurerm_synapse_workspace resource, set managed_virtual_network_enabled to true.

References:
https://learn.microsoft.com/en-us/azure/synapse-analytics/security/synapse-workspace-managed-vnet
https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/synapse_workspace#managed_virtual_network_enabled