Fixes widget extensons not rendering in the widget

Adds the widget extension container which is used to
render any registered extensions.

app/assets/javascripts/vue_merge_request_widget/components/extensions/container.js

@@ -8,12 +8,14 @@ export default {
     },
   },
   render(h) {
+    if (extensions.length === 0) return null;
+
     return h(
       'div',
       {},
       extensions.map((extension) =>
         h(extension, {
-          props: extensions[0].props.reduce(
+          props: extension.props.reduce(
             (acc, key) => ({
               ...acc,
               [key]: this.mr[key],

app/assets/javascripts/vue_merge_request_widget/mr_widget_options.vue

@@ -38,7 +38,7 @@ import ReadyToMergeState from './components/states/ready_to_merge.vue';
 import ShaMismatch from './components/states/sha_mismatch.vue';
 import UnresolvedDiscussionsState from './components/states/unresolved_discussions.vue';
 import WorkInProgressState from './components/states/work_in_progress.vue';
-// import ExtensionsContainer from './components/extensions/container';
+import ExtensionsContainer from './components/extensions/container';
 import eventHub from './event_hub';
 import mergeRequestQueryVariablesMixin from './mixins/merge_request_query_variables';
 import getStateQuery from './queries/get_state.query.graphql';
@@ -52,7 +52,7 @@ export default {
   },
   components: {
     Loading,
-    // ExtensionsContainer,
+    ExtensionsContainer,
     'mr-widget-header': WidgetHeader,
     'mr-widget-suggest-pipeline': WidgetSuggestPipeline,
     MrWidgetPipelineContainer,
@@ -496,7 +496,7 @@ export default {
           </template>
         </mr-widget-alert-message>
       </div>
-      <!-- <extensions-container :mr="mr" /> -->
+      <extensions-container :mr="mr" />
       <grouped-codequality-reports-app
         v-if="shouldRenderCodeQuality"
         :head-blob-path="mr.headBlobPath"

ee/app/assets/javascripts/vue_merge_request_widget/mr_widget_options.vue

@@ -305,6 +305,7 @@ export default {
           </template>
         </mr-widget-alert-message>
       </div>
+      <extensions-container :mr="mr" />
       <blocking-merge-requests-report :mr="mr" />
       <grouped-codequality-reports-app
         v-if="shouldRenderCodeQuality"