Delete resource group on workspace deletion even if it has "lingering" resources.

Occasionally Azure resources are left in a resource group and are not being tracked by Terraform state/TRE resources. This prevents deletion of the workspace and requires and Azure admin to interveen. We could set the feature flag `prevent_deletion_if_contains_resources = false` within the `features` of the AzureRM provider to enable the workspaces to be deleted.

