Add Webpack setup for Jira Connect app

- Create a separate JS bundle for jira_connect
- Add ESLint

app/assets/javascripts/jira_connect/.eslintrc.yml

+globals:
+  AP: readonly
+rules:
+  '@gitlab/require-i18n-strings': off
+  '@gitlab/vue-require-i18n-strings': off

app/assets/javascripts/jira_connect/components/app.vue

+<script>
+export default {};
+</script>
+
+<template>
+  <div></div>
+</template>

app/assets/javascripts/jira_connect/index.js

+import Vue from 'vue';
+import App from './components/app.vue';
+
+function initJiraConnect() {
+  const el = document.querySelector('.js-jira-connect-app');
+
+  return new Vue({
+    el,
+    render(createElement) {
+      return createElement(App, {});
+    },
+  });
+}
+
+document.addEventListener('DOMContentLoaded', initJiraConnect);

app/assets/stylesheets/page_bundles/jira_connect.scss

-@import 'framework/variables';
+@import 'mixins_and_variables_and_functions';
+// We should only import styles that we actually use.
+// @import '@gitlab/ui/src/scss/gitlab_ui';
 
 $atlaskit-border-color: #dfe1e6;
 

app/views/jira_connect/subscriptions/index.html.haml

@@ -21,6 +21,8 @@
     .gl-mt-5
       %p Note: this integration only works with accounts on GitLab.com (SaaS).
   - else
+    .js-jira-connect-app
+
     %form#add-subscription-form.subscription-form{ action: jira_connect_subscriptions_path }
       .ak-field-group
         %label
@@ -57,5 +59,8 @@
     or enable cross-site cookies in your browser when adding a namespace.
     %a{ href: 'https://gitlab.com/gitlab-org/gitlab/-/issues/263509', target: '_blank', rel: 'noopener noreferrer' } Learn more
 
+= webpack_bundle_tag 'performance_bar' if performance_bar_enabled?
+= webpack_bundle_tag 'jira_connect_app'
+
 = page_specific_javascript_tag('jira_connect.js')
 - add_page_specific_style 'page_bundles/jira_connect'

config/webpack.config.js

@@ -82,6 +82,7 @@ function generateEntries() {
     // sentry: './sentry/index.js', Temporarily commented out to investigate performance: https://gitlab.com/gitlab-org/gitlab/-/issues/251179
     performance_bar: './performance_bar/index.js',
     chrome_84_icon_fix: './lib/chrome_84_icon_fix.js',
+    jira_connect_app: './jira_connect/index.js',
   };
 
   return Object.assign(manualEntries, autoEntries);