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/meta/argument_specs.yml

@@ -45,7 +45,16 @@ argument_specs:
       garage_webui_domain:
         type: str
         default: console.storage.local.test
-        description: Hostname serving the WebUI console.
+        description: Canonical WebUI console hostname (first entry of C(garage_webui_domains)).
+      garage_webui_domains:
+        type: list
+        elements: str
+        default: ['console.storage.local.test']
+        description:
+          - FQDNs the WebUI console router accepts. The first entry is the
+            canonical public domain; further entries cover internal
+            C(*.int.*) names so a DMZ reverseproxy can use a C(backend_host)
+            whose cert SAN matches. Defaults to just C(garage_webui_domain).
 
       garage_webui_enabled:
         type: bool