Subjects the broker may create streamName with when the stream is absent on the server.
There is deliberately NO default and no catch-all: NATS refuses a stream
capturing every subject unless it is created with no_ack: true, and
no_ack makes every JetStream publish reject unobserved (X28-2). Supplied
and the stream is absent → the broker creates it with exactly these
subjects. Absent and the stream is absent → startup rejects with
JetStreamStreamError, naming the stream and both remedies (create the
stream out of band, or supply this option). An existing stream is never
touched either way.