Add frontend resource i18n strings

app/assets/javascripts/performance_bar/index.js

-/* eslint-disable @gitlab/require-i18n-strings */
 import Vue from 'vue';
 import axios from '~/lib/utils/axios_utils';
 import { numberToHumanSize } from '~/lib/utils/number_utils';

locale/gitlab.pot

@@ -22634,9 +22634,15 @@ msgstr ""
 msgid "Performance optimization"
 msgstr ""
 
+msgid "PerformanceBar|Backend"
+msgstr ""
+
 msgid "PerformanceBar|Bullet notifications"
 msgstr ""
 
+msgid "PerformanceBar|Dom content loaded"
+msgstr ""
+
 msgid "PerformanceBar|Download"
 msgstr ""
 
@@ -22646,6 +22652,9 @@ msgstr ""
 msgid "PerformanceBar|External Http calls"
 msgstr ""
 
+msgid "PerformanceBar|First contentful paint"
+msgstr ""
+
 msgid "PerformanceBar|Frontend resources"
 msgstr ""