Ensure public access is disabled for Azure MariaDB Server

Allowing unrestricted, public access to cloud services could open an application up to external attack. Disallowing this access is typically considered best practice.

In Azure Console -

1. Open the Azure Portal and go to Azure Database for MariaDB servers.
2. Choose the MariaDB server you wish to edit.
3. Under Connection Security, set Deny public network access to Yes.
4. Select Save

In Terraform -

1. In the azurerm_mariadb_server resource, set public_network_access_enabled to false.

References:
https://learn.microsoft.com/en-us/azure/mariadb/howto-deny-public-network-access
https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/mariadb_server#public_network_access_enabled