The declarative form of one IMessageBroker.subscribe() call — the entry
an application writes instead of calling subscribe() imperatively after
start().
readonly
topic: string
The topic to subscribe to (the subscribe() topic argument).
readonly
handler: MessageHandler
Invoked per delivered message, exactly as the imperative subscribe() accepts.
readonly
optional
options: SubscribeOptions
Consumer-group configuration, exactly as the imperative subscribe() accepts.