Add a new feature flag to switch environment logs page to vue

- Add switching to haml
- Add switch to gon.features in browser
- Add feature flag to feature/spec

ee/app/assets/javascripts/logs/logs_bundle.js

+export default () => {};

ee/app/assets/javascripts/pages/projects/environments/logs/index.js

+import logsBundle from 'ee/logs/logs_bundle';
 import KubernetesLogs from '../../../../kubernetes_logs';
 
-document.addEventListener('DOMContentLoaded', () => {
+if (gon.features.environmentLogsUseVueUi) {
+  document.addEventListener('DOMContentLoaded', logsBundle);
+} else {
+  document.addEventListener('DOMContentLoaded', () => {
     const kubernetesLogContainer = document.querySelector('.js-kubernetes-logs');
     const kubernetesLog = new KubernetesLogs(kubernetesLogContainer);
-
     kubernetesLog.getData();
-});
+  });
+}

ee/app/controllers/ee/projects/environments_controller.rb

@@ -9,6 +9,9 @@ module EE
         before_action :authorize_read_pod_logs!, only: [:logs]
         before_action :environment_ee, only: [:logs]
         before_action :authorize_create_environment_terminal!, only: [:terminal]
+        before_action do
+          push_frontend_feature_flag(:environment_logs_use_vue_ui)
+        end
       end
 
       def logs

ee/app/views/projects/environments/logs.html.haml

-.js-kubernetes-logs{ data: environment_logs_data(@project, @environment) }
+- if Feature.enabled?('environment_logs_use_vue_ui')
+  #environment-logs{ data: environment_logs_data(@project, @environment) }
+- else
+  .js-kubernetes-logs{ data: environment_logs_data(@project, @environment) }
     .build-page-pod-logs
       .build-trace-container.prepend-top-default
         .top-bar.js-top-bar.d-flex

ee/spec/features/projects/environments_pod_logs_spec.rb

@@ -15,6 +15,7 @@ describe 'Environment > Pod Logs', :js do
 
   before do
     stub_licensed_features(pod_logs: true)
+    stub_feature_flags(environment_logs_use_vue_ui: false)
 
     create(:cluster, :provided_by_gcp, environment_scope: '*', projects: [project])
     create(:deployment, :success, environment: environment)