chore: add default_version and codeowner_team to .repo-metadata.json (#92)

By default the code owner will be googleapis/yoshi-python. This change is needed for the following synthtool PRs.

googleapis/synthtool#1201
googleapis/synthtool#1114

Author: parthea

packages/google-cloud-notebooks/.repo-metadata.json

@@ -9,5 +9,7 @@
     "library_type": "GAPIC_AUTO",
     "repo": "googleapis/python-notebooks",
     "distribution_name": "google-cloud-notebooks",
-    "api_id": "notebooks.googleapis.com"
-  }  
+    "api_id": "notebooks.googleapis.com",
+    "default_version": "v1",
+    "codeowner_team": ""
+}