Updated ees/ers implementation to use the jetstream package which
separates the jetstream context from Core NATS.
Removed the jsOpts fields from the NatsEE struct. We are now using the
jetStreamMaxWait option directly through a timeout context.
Added streamName option for NATS reader since it is now required to be
specified when creating a consumer (it is not inferred based on subject
anymore).
Updated nats ers integration test.
Removed deprecated birpc unit test.
Updated tests to also use the new jetstream package.
Updated tests to start the nats-server using their official driver
instead of using the std go exec package. time.Sleeps are now not
required anymore to wait for the server.
In test configurations for nats readers, made sure that natsStreamName
option is populated. It is now required for consumers to know where to
subscribe.
Fixed potential panic that happened when jetstreamMaxWait option would
not be set.
