docs: Prepare for new sub tree

See #11925

docs/content/en/methods/page/Slug.md

@@ -1,25 +0,0 @@
----
-title: Slug
-description: Returns the URL slug of the given page as defined in front matter.
-categories: []
-keywords: []
-action:
-  related: []
-  returnType: string
-  signatures: [PAGE.Slug]
----
-
-{{< code-toggle file=content/recipes/spicy-tuna-hand-rolls.md fm=true >}}
-title = 'How to make spicy tuna hand rolls'
-slug = 'sushi'
-{{< /code-toggle >}}
-
-This page will be served from:
-
-    https://example.org/recipes/sushi
-
-To get the slug value within a template:
-
-```go-html-template
-{{ .Slug }} → sushi
-```