[ForumTopics] Add a confirmation before marking topics as read

app/javascript/src/javascripts/forum_topics.js

@@ -0,0 +1,13 @@
+let ForumTopic = {};
+
+ForumTopic.init_mark_all_as_read = function () {
+  $("#subnav-mark-all-as-read-link").on("click.danbooru", () => {
+    return confirm("Are you sure that you want to mark all forum topics as read?");
+  });
+};
+
+$(() => {
+  ForumTopic.init_mark_all_as_read();
+});
+
+export default ForumTopic;