Horizon is not installed in AIO deployment

[Hector Vido]

I am installing Openstack AIO from tag "stable/2023.2" and noticed that an installation method distro/lxc with scenario as "aio_metal" do not install Horizon frontend.

Almost all tasks from "os-horizon-install.yml" are skipped. I managed to make it work by changing the inventory as the follows:

```
[horizon_all]
localhost ansible_connection=local ansible_host=localhost is_metal=true horizon_backend_ssl=0 horizon_external_ssl=0 horizon_listen_ports='{"http" : "8080"}'
```

After running the playbook I modified /etc/haproxy/haproxy.conf adding the correct port to the backend:

```
backend horizon-back
...
    server localhost localhost:8080 check port 8080 inter 12000 rise 3 fall 3
```

Looks like the "metal" option exported in $SCENARIO was not configured inside horizon tasks.

Best,

[Dmitriy Rabotyagov (noonedeadpunk)]

Hey,

Eventually, horizon is skipped for metal deployments "by design", or better say - due to legacy decisions.

If you want to have horizon on metal AIO, you need to add `horizon` to scenario list explicitly.

Alternatively, you'd need to create /etc/openstack_deploy/conf.d/horizon.yml with content like here:
https://opendev.org/openstack/openstack-ansible/src/branch/master/etc/openstack_deploy/conf.d/horizon.yml.aio

After that you should be able to rerun os-horizon-install.yml playbook.