Add task active duration migration

apiserver/mongo/migrations/0.17.1.py

@@ -0,0 +1,24 @@
+from pymongo.database import Database
+
+
+def _add_active_duration(db: Database):
+    active_duration = "active_duration"
+    query = {active_duration: {"$eq": None}}
+    collection = db["task"]
+    for doc in collection.find(
+        filter=query, projection=[active_duration, "started", "last_update"]
+    ):
+        started = doc.get("started")
+        last_update = doc.get("last_update")
+        if started and last_update and doc.get(active_duration) is None:
+            collection.update_one(
+                {"_id": doc["_id"]},
+                {"$set": {active_duration: (last_update - started).total_seconds()}},
+            )
+
+
+def migrate_backend(db: Database):
+    """
+    Add active_duration field to tasks
+    """
+    _add_active_duration(db)