website/docs: improve traefik standalone docs (#4493)

* Create _traefik_standalone_single_application.md 

Example for Authentik Single Application Proxy with Service example because this was unclear for many users and if you dont create a middleware for every application you get the error "no app for hostname". 

Signed-off-by: support-tt <61587422+support-tt@users.noreply.github.com>

* Update _traefik_standalone_single_application.md

Signed-off-by: support-tt <61587422+support-tt@users.noreply.github.com>

* rename to old file

Signed-off-by: Jens Langhammer <jens@goauthentik.io>

---------

Signed-off-by: support-tt <61587422+support-tt@users.noreply.github.com>
Signed-off-by: Jens Langhammer <jens@goauthentik.io>
Co-authored-by: Jens Langhammer <jens@goauthentik.io>

website/docs/providers/proxy/_traefik_standalone.md

@@ -23,9 +23,18 @@ http:
             middlewares:
                 - name: authentik
             priority: 10
-            services: # Unchanged
+            services: app
         default-router-auth:
             match: "Host(`app.company`) && PathPrefix(`/outpost.goauthentik.io/`)"
             priority: 15
-            services: http://outpost.company:9000/outpost.goauthentik.io
+            services: authentik
+    services:
+        app:
+            loadBalancer:
+                servers:
+                    - url: http://ipp.internal
+        authentik:
+            loadBalancer:
+                servers:
+                    - url: http://outpost.company:9000/outpost.goauthentik.io
 ```