chore: add authentik_login_user_fields to allow showing custom fields, or removing them

e.g when using social + local logins

roles/authentik/templates/blueprints/blueprint-login-sources.yaml.j2

@@ -4,14 +4,19 @@ metadata:
   name: "login-sources"
   labels:
     blueprints.goauthentik.io/instantiate: "true"
-    blueprints.goauthentik.io/description: "Set sources on the identification stage"
+    blueprints.goauthentik.io/description: "Set sources and user fields on the identification stage"
 
 entries:
   - model: authentik_stages_identification.identificationstage
     identifiers:
       name: "{{ authentik_identification_stage_name }}"
     attrs:
-      # NOTE: this SETS the sources list (it doesn’t append).
+      # Local login fields (username, email, upn)
+      user_fields:
+{% for field in authentik_login_user_fields %}
+        - {{ field }}
+{% endfor %}
+      # OAuth/social login sources
       sources:
 {% for src_id in authentik_login_source_ids %}
         - !KeyOf {{ src_id }}