fix(operator): Clean up scaling cooldowns

# Issue

The table `scalingcooldowns` will gain an entry once an app is scaled.
This entry is never removed, thus a resource leak is created.

The table can get so big, that a simple select starts to take time (as
there is no index on the table).

# Fix

The table is now periodically cleaned by the `operator`.

.envrc

@@ -21,3 +21,5 @@ if has bbl && [[ -d "$bbl_state_dir" ]]
 then
     eval "$(bbl print-env --state-dir "$bbl_state_dir")"
 fi
+
+export DBURL="postgres://postgres:postgres@localhost/autoscaler"