feat(garage,authentik): console multi-domain + standalone proxy outpost

Two related additions for gating a cross-host service (garage WebUI on a
storage host) behind authentik without breaking on TLS or X-Forwarded-Host:

garage role:
- Add garage_webui_domains (list), mirroring garage_s3_domains. The
  console router now accepts every entry, so a DMZ reverseproxy can use a
  backend_host whose cert SAN matches an internal *.int.* name instead of
  connecting by IP (which fails acme cert verification). Defaults to the
  single garage_webui_domain so existing inventories are unaffected.

authentik_outpost_proxy role (new):
- Standalone proxy (ForwardAuth) outpost, modelled on authentik_outpost_ldap.
  Co-locate it with the protected service so the ForwardAuth subrequest
  reaches authentik over the local docker network. The embedded outpost
  only works for services on the authentik host: a cross-host subrequest
  routed through an extra reverse-proxy hop arrives with a polluted
  X-Forwarded-Host (port/comma-appended), which the outpost no longer
  matches against the provider's external_host (404).

roles/garage/templates/docker-compose.yml.j2

@@ -49,7 +49,7 @@ services:
     labels:
       - traefik.enable=true
       - traefik.docker.network={{ garage_traefik_network }}
-      - traefik.http.routers.{{ garage_service_name }}-console.rule=Host(`{{ garage_webui_domain }}`)
+      - traefik.http.routers.{{ garage_service_name }}-console.rule={% for d in garage_webui_domains %}Host(`{{ d }}`){% if not loop.last %} || {% endif %}{% endfor +%}
 {% if garage_use_ssl %}
       - traefik.http.routers.{{ garage_service_name }}-console.entrypoints=websecure
       - traefik.http.routers.{{ garage_service_name }}-console.tls=true