Wire up the Oban Pro Smart engine in base + runtime config and add the
Pro migration (oban_producers, oban_crons, oban_queues tables + the
v1.6 partition/workflow index additions on oban_jobs).
On the Smart engine the era5_batch queue now has a global_limit of 4
in-flight jobs across the cluster and a rate_limit of 10 jobs per hour
so slow Copernicus CDS submit/poll cycles can't exhaust our daily
request budget when a backfill kicks off.
