docs: add repository, enabled, required frontmatter to all plugin docs

Added repository, enabled, and required fields to the frontmatter of
all 44 plugin documentation files. Updated Plugins.base to include
these columns, matching the information previously in the manual tables.
Also filtered out internal plugins (Assets, Static, ComponentResources,
NotFoundPage) from the base query.

docs/plugins/Explorer.md

@@ -3,6 +3,9 @@ title: Explorer
 tags:
   - plugin/component
 image:
+repository: "quartz-community/explorer"
+enabled: true
+required: false
 ---
 
 File tree explorer sidebar.