Make default user services configurable by admin

app/views/admin/settings/registrations/show.html.erb

@@ -9,18 +9,35 @@
         <%= render partial: "admin/settings/errors", locals: { errors: @errors } %>
       <% end %>
 
-      <label class="block">
-        <p class="font-bold mb-1">Reserved usernames</p>
-        <p class="text-gray-500">
-          These usernames cannot be registered as accounts:
-        </p>
-        <%= f.text_area :reserved_usernames,
-          value: Setting.reserved_usernames.join("\n"),
-          class: "h-44 mb-2" %>
-        <p class="text-sm text-gray-500">
-          One username per line
-        </p>
-      </label>
+      <ul role="list">
+        <%= render FormElements::FieldsetComponent.new(
+              title: "Reserved usernames",
+              description: "These usernames cannot be registered as accounts."
+            ) do %>
+          <%= f.text_area :reserved_usernames,
+            value: Setting.reserved_usernames.join("\n"),
+            class: "h-44 w-60" %>
+          <p class="text-sm text-gray-500">
+            One username per line
+          </p>
+        <% end %>
+        <li>
+          <p class="font-bold mb-1">Default services</p>
+          <p class="text-gray-500">
+            These services are enabled for new users by default after signup.
+          </p>
+          <div class="flex flex-wrap gap-x-6 gap-y-2">
+            <% Setting.available_services.each do |option| %>
+              <div class="md:inline-block">
+                <%= f.check_box :default_services,
+                  { multiple: true, checked: Setting.default_services.include?(option) },
+                  option, nil %>
+                <%= f.label "default_services_#{option.parameterize}", service_human_name(option) %>
+              </div>
+            <% end %>
+          </div>
+        </li>
+      </ul>
     </section>
 
     <section>