docs(xo): refactor navbar navigation to create a unified documentation ecosystem (#10067)

* docs(xo): overhaul navbar to create a unified doc ecosystem

- Clean up the navbar by dropping the redundant GitHub link (retained in footer).
- Relocate "Blog" to the "What's new in XO 6" sidebar.
- Introduce direct navbar links for XCP-ng and Vates VMS.
- Rename "Documentation" to "Xen Orchestra".

This aligns the navigation layout across our three documentation sites, allowing readers to smoothly transition between ecosystems with a fully unified experience.

Signed-off-by: Thomas Moraine <thomas.moraine@vates.tech>

* docs(xo): move home link from header to footer

To make the navbar cleaner and make space
for the links to the other documentation websites
We're moving the Home link from the header to the footer
and renaming the link to 'About Xen Orchestra'.
Also, we're displaying the 'What's new in XO 6' section again
which now contains a link to the XO blog

Signed-off-by: Thomas Moraine <thomas.moraine@vates.tech>

docs/src/css/custom.css

@@ -29,6 +29,11 @@
   --docusaurus-highlighted-code-line-bg: rgba(0, 0, 0, 0.3);
 }
 
+/* Make all text links inside the navbar bold */
+.navbar__item {
+  font-weight: bold;
+}
+
 [data-theme='dark'] .DocSearch {
   --docsearch-text-color: var(--ifm-font-color-base);
   --docsearch-muted-color: var(--ifm-color-secondary-darkest);