Add registered fields to resource_admin (#10941)

app/controllers/resource_admin/users_controller.rb

@@ -79,6 +79,8 @@ module ResourceAdmin
         reputation_modifier
         saw_onboarding
         scholar_email
+        registered
+        registered_at
       ]
     end
   end

app/dashboards/user_dashboard.rb

@@ -19,6 +19,8 @@ class UserDashboard < Administrate::BaseDashboard
     website_url: Field::String,
     created_at: Field::DateTime,
     updated_at: Field::DateTime,
+    registered: Field::Boolean,
+    registered_at: Field::DateTime,
     articles: Field::HasMany,
     comments: Field::HasMany,
     reputation_modifier: Field::Number,
@@ -70,6 +72,8 @@ class UserDashboard < Administrate::BaseDashboard
     name
     username
     email
+    registered
+    registered_at
     twitter_username
     github_username
     profile_image