Add v1.6.0 mongodb migration

apiserver/mongo/migrations/1_6_0.py

@@ -0,0 +1,12 @@
+from pymongo.collection import Collection
+from pymongo.database import Database
+
+
+def migrate_backend(db: Database):
+    projects: Collection = db["project"]
+    for doc in projects.find({"basename": None}):
+        name: str = doc["name"]
+        _, _, basename = name.rpartition("/")
+        projects.update_one(
+            {"_id": doc["_id"]}, {"$set": {"basename": basename}},
+        )