Add webpacker and use it for new_design

app/javascript/new_design/champs/siret.js

@@ -0,0 +1,34 @@
+addEventListener('turbolinks:load', () => {
+  $('[data-siret]').on('input', evt => {
+    const input = $(evt.target);
+    const value = input.val();
+    const url = input.attr('data-siret');
+
+    switch (value.length) {
+      case 0:
+        $.get(`${url}?siret=blank`);
+        break;
+      case 14:
+        input.attr('disabled', 'disabled');
+        $('.spinner').show();
+        $.get(`${url}?siret=${value}`).then(
+          () => {
+            input.removeAttr('data-invalid');
+            input.removeAttr('disabled');
+            $('.spinner').hide();
+          },
+          () => {
+            input.removeAttr('disabled');
+            input.attr('data-invalid', true);
+            $('.spinner').hide();
+          }
+        );
+        break;
+      default:
+        if (!input.attr('data-invalid')) {
+          input.attr('data-invalid', true);
+          $.get(`${url}?siret=invalid`);
+        }
+    }
+  });
+});