Add front matter that informs Hugo that the Grafana content is versioned (#74259)

This is necessary to allow version inference in CI builds.
Shortcodes like `docs/reference` and `docs/shared` use version inference to avoid the writer having to hardcode specific versions or use relative paths within the documentation set.

Signed-off-by: Jack Baldry <jack.baldry@grafana.com>

scripts/drone/steps/lib.star

@@ -788,6 +788,7 @@ def build_docs_website_step():
         "image": images["docs"],
         "commands": [
             "mkdir -p /hugo/content/docs/grafana/latest",
+            "echo -e '---\\nredirectURL: /docs/grafana/latest/\\ntype: redirect\\nversioned: true\\n---\\n' > /hugo/content/docs/grafana/_index.md",
             "cp -r docs/sources/* /hugo/content/docs/grafana/latest/",
             "cd /hugo && make prod",
         ],