Create workspace dropdown returns `Unnamed` for templates with no display name

i have templates that only have API names such as `azure-pod-template`, with no display name. this causes a bad experience with the new Create Workspace button:

<img width="389" alt="Screenshot 2023-10-11 at 4 16 43 PM" src="https://github.com/coder/coder/assets/9683576/13371620-8ccd-4d9f-b394-9bbad910d401">

we should default to the template API name if there is no display name set.
