Incorrect template for registry auth

[Danny Cocks]

When configuring the containerd custom_registries config with an entry including a password, and the `config_version` option is to `v2` (the default for channel 1.24 and beyond) the charm renders the containerd config.toml file incorrectly.

The error in the template (templates/config_v2.toml) is here:

        [plugins."io.containerd.grpc.v1.cri".registry.mirrors."{{ registry.host }}"]
...
        [plugins."io.containerd.grpc.v1.cri".registry.configs."{{ registry.url }}".auth]

The second line above should read `regsitry.host` instead of `registry.url`.