[doc] Message redelivery and acknowledgement

[Jennifer88huang-zz]

Is your feature request related to a problem? Please describe.
In the current messaging docs, there is no content related to message redelivery and acknowledgement.

Describe the solution you'd like
Add clear and concise description of message redelivery and acknowledgement.

[lhotari]

In the current messaging docs, there is no content related to message redelivery and acknowledgement.

Yes this is a gap. It might help to reference the "Message retention and expiry" docs ( https://pulsar.apache.org/docs/en/cookbooks-retention-expiry/ ) since that is related to redelivery and acknowledgement.