fix(docs): Add repository field for npm provenance verification

NPM provenance verification requires the package.json repository
URL to match the GitHub repository the action is running from.

docs/package.json

@@ -11,6 +11,10 @@
     "publishConfig": {
         "access": "public"
     },
+    "repository": {
+        "type": "git",
+        "url": "https://github.com/vendurehq/vendure"
+    },
     "files": [
         "dist",
         "docs",