Admin users page: filter by username

Allow admins to filter the user list/index by username (partial matches
allowed)

app/controllers/admin/users_controller.rb

@@ -12,7 +12,11 @@ class Admin::UsersController < Admin::BaseController
     @contributors = ldap.search_users(:memberStatus, :contributor, :cn) if @show_contributors
     @sustainers   = ldap.search_users(:memberStatus, :sustainer, :cn) if @show_sustainers
     @admins       = ldap.search_users(:admin, true, :cn)
-    @pagy, @users = pagy(User.where(ou: ou).order(cn: :asc))
+
+    @username = params[:username].presence
+    users_scope = User.where(ou: ou).order(cn: :asc)
+    users_scope = users_scope.where("cn LIKE ?", "%#{User.sanitize_sql_like(@username.downcase)}%") if @username
+    @pagy, @users = pagy(users_scope)
 
     @stats = {
       users_confirmed: User.where(ou: ou).confirmed.count,

app/views/admin/users/index.html.erb

@@ -30,6 +30,11 @@
     <% end %>
   </section>
 
+  <section>
+    <%= render partial: "admin/username_search_form",
+               locals: { path: admin_users_path } %>
+  </section>
+
   <section>
     <table class="divided mb-8">
       <thead>