deposit/conf: Add back the storage key config

The (django) migration steps are happening during the docker `up` phase.
Deposit wise, one migration script (`deposit.0018_migrate_swhids`) is requiring
a storage. As this key got removed, this makes that migration step fail.

This commit adds back that storage key.

docker/conf/deposit.yml

@@ -3,6 +3,11 @@ scheduler:
   args:
     url: http://swh-scheduler:5008
 
+storage:
+  cls: remote
+  args:
+    url: http://swh-storage:5002/
+
 storage_metadata:
   cls: remote
   args: