Scaffold FE structure for work items

app/assets/javascripts/pages/projects/work_items/index/index.js

+import { initWorkItemsRoot } from '~/work_items/index';
+
+initWorkItemsRoot();

app/assets/javascripts/work_items/components/app.vue

+<script>
+export default {
+  name: 'WorkItemRoot',
+};
+</script>
+
+<template>
+  <div></div>
+</template>

app/assets/javascripts/work_items/index.js

+import Vue from 'vue';
+import App from './components/app.vue';
+
+export const initWorkItemsRoot = () => {
+  const el = document.querySelector('#js-work-items');
+
+  return new Vue({
+    el,
+    render(createElement) {
+      return createElement(App);
+    },
+  });
+};

app/controllers/projects/work_items_controller.rb

+# frozen_string_literal: true
+
+class Projects::WorkItemsController < Projects::ApplicationController
+  before_action do
+    push_frontend_feature_flag(:work_items, project, default_enabled: :yaml)
+  end
+
+  feature_category :not_owned
+
+  def index
+  end
+end

app/views/projects/work_items/index.html.haml

+- page_title s_('WorkItem|Work Items')
+
+#js-work-items

config/feature_flags/development/work_items.yml

+---
+name: work_items
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/69085
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/339664
+milestone: '14.3'
+type: development
+group: group::project management
+default_enabled: false

config/routes/project.rb

@@ -354,6 +354,8 @@ constraints(::Constraints::ProjectUrlConstrainer.new) do
           get 'details', on: :member
         end
 
+        resources :work_items, only: [:index]
+
         resource :tracing, only: [:show]
 
         post 'incidents/integrations/pagerduty', to: 'incident_management/pager_duty_incidents#create'
@@ -601,7 +603,6 @@ constraints(::Constraints::ProjectUrlConstrainer.new) do
                                             :vulnerability_feedback, :security, :dependencies, :issues,
                                             :pipelines, :pipeline_schedules, :runners, :snippets)
     end
-
     # rubocop: disable Cop/PutProjectRoutesUnderScope
     resources(:projects,
               path: '/',

locale/gitlab.pot

@@ -38033,6 +38033,9 @@ msgstr ""
 msgid "Work in progress Limit"
 msgstr ""
 
+msgid "WorkItem|Work Items"
+msgstr ""
+
 msgid "Would you like to create a new branch?"
 msgstr ""