feat(v2): absolute slugs and slug resolution system (#3084)

* rework slug to allow absolute slugs and slug resolution

* add slug metadata tests

* refactor docs metadata test + fix slug bugs

* fix tests

* fix docs tests failing due to randomness + update snapshot

* add test for addLeadingSlash

packages/docusaurus-plugin-content-docs/src/index.ts

@@ -436,7 +436,10 @@ Available document ids=
       // to be by version and pick only needed base metadata.
       if (versioning.enabled) {
         const docsMetadataByVersion = groupBy(
-          Object.values(content.docsMetadata),
+          // sort to ensure consistent output for tests
+          Object.values(content.docsMetadata).sort((a, b) =>
+            a.id.localeCompare(b.id),
+          ),
           'version',
         );