Announcement banner for site change (#5910)

Author: kimsauce

docusaurus.config.js

@@ -257,6 +257,12 @@ module.exports = {
       { property: 'og:image:height', content: '628' },
       { property: 'og:image:alt', content: 'Sumo Logic Docs' },
     ],
+    announcementBar: {
+      id: 'domain',
+      content: '<b>We’ve moved!</b> Our docs are now at <a href="https://www.sumologic.com/help">sumologic.com/help</a>. Redirects are in place, but don’t forget to update your bookmarks.',
+      backgroundColor: '#b0eefe',
+      textColor: '#091E42',
+    },
     imageZoom: {
       selector: '.markdown :not(a) > img',
       // Optional medium-zoom options