Created an admin form for required ci template

Created a form for the user to select an instance template
for CI configuration to require that pipeline to run
after every pipeline on the instance.

app/assets/javascripts/pages/admin/application_settings/ci_cd/ci_template.js

+import $ from 'jquery';
+
+export default class CiTemplate {
+  constructor() {
+    this.$input = $('#required_template_name');
+    this.$dropdown = $('.js-ci-template-dropdown');
+    this.$dropdownToggle = this.$dropdown.find('.dropdown-toggle-text');
+
+    this.initDropdown();
+  }
+
+  initDropdown() {
+    this.$dropdown.glDropdown({
+      data: this.formatDropdownList(),
+      selectable: true,
+      filterable: true,
+      allowClear: true,
+      toggleLabel: item => item.name,
+      search: {
+        fields: ['name'],
+      },
+      clicked: clickEvent => this.updateInputValue(clickEvent),
+      text: item => item.name,
+    });
+
+    this.setDropdownToggle();
+  }
+
+  formatDropdownList() {
+    return {
+      Reset: [
+        {
+          name: 'None',
+          id: '',
+        },
+        'divider',
+      ],
+      ...this.$dropdown.data('data'),
+    };
+  }
+
+  setDropdownToggle() {
+    const initialValue = this.$input.val();
+
+    if (initialValue) {
+      this.$dropdownToggle.text(initialValue);
+    }
+  }
+
+  updateInputValue({ selectedObj, e }) {
+    e.preventDefault();
+
+    this.$input.val(selectedObj.id);
+  }
+}

app/assets/javascripts/pages/admin/application_settings/ci_cd/index.js

+import CiTemplate from './ci_template';
+
+document.addEventListener('DOMContentLoaded', () => new CiTemplate());

app/views/admin/application_settings/_required_pipeline.html.haml

+= form_for @application_setting, url: admin_application_settings_path(anchor: 'js-required-pipeline-settings'), html: { class: 'fieldset-form' } do |f|
+  = form_errors(@application_setting)
+
+  %fieldset
+    .form-group
+      = f.label :shared_runners_text, s_('AdminSettings|Select a pipeline configuration file'), class: 'text-muted'
+      = dropdown_tag("Select a template", options: { toggle_class: 'js-ci-template-dropdown w-100', title: "Apply a template", filter: true, placeholder: "Filter", data: { data: gitlab_ci_ymls(nil) } } )
+      = f.text_field :shared_runners_text, value: @application_setting.shared_runners_text, id: 'required_template_name', class: 'hidden'
+
+  = f.submit _('Save changes'), class: "btn btn-success"

app/views/admin/application_settings/ci_cd.html.haml

@@ -13,6 +13,17 @@
   .settings-content
     = render 'ci_cd'
 
+%section.settings.as-required-pipeline.no-animate#js-required-pipeline-settings{ class: ('expanded' if expanded_by_default?)}
+  .settings-header
+    %h4
+      = _('Required pipeline configuration')
+    %button.btn.btn-default.js-settings-toggle{ type: 'button' }
+      = expanded_by_default? ? _('Collapse') : _('Expand')
+    %p
+      = ('Set an instance-wide auto included pipeline configuration. This pipeline configuration will be run after the project\'s own configuration.')
+  .settings-content
+    = render 'required_pipeline'
+
 - if Gitlab.config.registry.enabled
   %section.settings.as-registry.no-animate#js-registry-settings{ class: ('expanded' if expanded_by_default?) }
     .settings-header