fix: use absolute URL for RSS feed link to pass broken link checker

Docusaurus's broken link checker validates all internal paths (starting
with /) against its known routes. /blog/rss.xml is a generated file,
not a route, so the checker flagged it as broken on every page that
renders the footer — causing the CI build to fail.

Using the full absolute URL makes Docusaurus treat it as an external
link and skip the internal validation.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: stephanj

docusaurus/docusaurus.config.js

@@ -242,7 +242,7 @@ const config = {
               },
               {
                 label: 'RSS Feed',
-                href: '/blog/rss.xml',
+                href: 'https://genie.devoxx.com/blog/rss.xml',
               },
               {
                 label: 'GitHub',