Add webpacker and use it for new_design

app/javascript/new_design/messagerie.js

@@ -0,0 +1,25 @@
+export function scrollMessagerie() {
+  const $ul = $('.messagerie ul').first();
+
+  if ($ul.length) {
+    const $elementToScroll = $('.date.highlighted').first();
+
+    if ($elementToScroll.length != 0) {
+      scrollTo($ul, $elementToScroll);
+    } else {
+      scrollToBottom($ul);
+    }
+  }
+}
+
+function scrollTo($container, $scrollTo) {
+  $container.scrollTop(
+    $scrollTo.offset().top - $container.offset().top + $container.scrollTop()
+  );
+}
+
+function scrollToBottom($container) {
+  $container.scrollTop($container.prop('scrollHeight'));
+}
+
+addEventListener('turbolinks:load', scrollMessagerie);