feat(session): Add migration to delete terminated sessions

There is a new periodic job that will delete terminated sessions that
are older than one hour. However, since until now terminated sessions
were not deleted, the first time the job runs there could be a large
number of sessions that need deleted. This could have a negative impact
on a running cluster. To mitigate the operational risk, this adds a
migration to perform an initial delete while the cluster is offline.

internal/db/schema/migrations/oss/postgres/31/01_delete_termianted_sessions.up.sql

@@ -0,0 +1,12 @@
+begin;
+  delete from session
+  using session_state
+  where
+    session.public_id = session_state.session_id
+  and
+    session_state.state = 'terminated'
+  and
+    session_state.start_time < wt_sub_seconds_from_now(3600);
+
+  analyze;
+commit;