Use HTTP for localhost registry

Is there a way to use http (instead of https) for a localhost registry? Looks like the `default_registry` field in the settings file only accepts an origin so it fails to parse if prefixed by e.g. `http://`.

In the README I see that it's possible to use the http protocol for the OCI registry:

```
[registry."acme.registry.com".oci]
# This is an optional field that tells the OCI client to use a specific http protocol. If this is
# not set or not one of the accepted values of "http" or "https", then the default (https) will
# be used.
protocol = "https"
```

I tried using this for a warg registry but it didn't seem to work.