Add React Conf announcement bar (facebook#4560)

Author: mattcarrollcode

website/docusaurus.config.ts

@@ -247,9 +247,9 @@ const config: Config = {
       respectPrefersColorScheme: true,
     },
     announcementBar: {
-      id: 'new-architecture',
+      id: 'react-conf',
       content:
-        'The New Architecture has arrived - <a target="_blank" rel="noopener noreferrer" href="/blog/2024/10/23/the-new-architecture-is-here">learn more</a>',
+        'Join us for React Conf on Oct 7-8. <a target="_blank" rel="noopener noreferrer" href="https://conf.react.dev">Learn more</a>.',
       backgroundColor: '#20232a',
       textColor: '#fff',
       isCloseable: false,