Ensure that admin user is disabled for Azure Container Registry

The default administrator user account should be disabled; it is considered best practice to ensure that these accounts are disabled for services that have them.

In Azure Console -

1. Open the Azure Portal and go to Container Registries.
2. Select the Container Registry you wish to edit.
3. Under Settings, choose Access keys.
4. Set the Admin user setting to Disabled.

In Terraform -

1. In the azurerm_container_registry resource, set admin_enabled to false.

References:
https://learn.microsoft.com/en-us/azure/container-registry/container-registry-authentication
https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/container_registry#admin_enabled