Add docusaurus monorepo to renovate config

Signed-off-by: Nick Slowinski <nick@nick-slowinski.de>

renovate.json

@@ -1,3 +1,15 @@
 {
-  "$schema": "https://docs.renovatebot.com/renovate-schema.json"
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "packageRules": [
+    {
+      "extends": "monorepo:docusaurus",
+      "groupName": "docusaurus monorepo",
+      "matchUpdateTypes": [
+        "digest",
+        "patch",
+        "minor",
+        "major"
+      ]
+    }
+  ]
 }