Provide Exponential backoff for retries in a JetStream Consumer

[ColinSullivan1]

Feature Request

Provide an exponential backoff (or equivalent) for retries with a JetStream Consumer.

Use Case:

At scale this will ease pressure on the system and applications that wait to acknowledge for various reasons (out of order messages, grouping messages in a transaction, etc) would behave better.

Proposed Change:

Add a consumer creation options that allows for exponential retry backoff over a period of time.

Who Benefits From The Change(s)?

Any user of NATS JetStream.

Alternative Approaches

Applications would specify a large number of max-redeliveries combined with ack wait and application side logic.

[andreib1]

If this is for pull, it is a duplicate of #2042

[derekcollison]

Nak with delay was implemented.