NATS: Revisit sync_interval settings for existing deployments

From https://docs.nats.io/running-a-nats-service/configuration#jetstream-server-settings, sync_interval can be tweaked to avoid losing data that hasn't been flushed to disk yet. It currently defaults to 2m - which may or may not be the right setting for some of our deployments. This issue warrants we revisit those settings and change them as necessary.