Add sitemaps for LXD docs (default, latest) (#2621)

Signed-off-by: Elijah Greenstein <elijah.greenstein@canonical.com>
Co-authored-by: Peter French <peter.french@canonical.com>

Author: elijahgreenstein

templates/sitemap-index.xml

@@ -39,6 +39,12 @@
   <sitemap>
     <loc>https://canonical.com/anbox-cloud/docs/doc-sitemap.xml</loc>
   </sitemap>
+  <sitemap>
+    <loc>https://canonical.com/lxd/docs/latest/sitemap.xml</loc>
+  </sitemap>
+  <sitemap>
+    <loc>https://canonical.com/lxd/docs/default/sitemap.xml</loc>
+  </sitemap>
   <sitemap>
     <loc>https://canonical.com/juju/docs/12-factor/latest/sitemap.xml</loc>
   </sitemap>