Add an API to configure the acknowledger about broadway

[josevalim]

This will call the configure/3 function in the acknowledger module with the ack_ref, ack_data, and user options. If configure/3 is not implemented (an optional callback), it will raise.

[mcrumm]

@josevalim Is the ack configuration going to be Broadway-specific, or Producer/Client-specific?

Google Cloud Pub/Sub has a very limited set of options: ack or modack (modify ack deadline). GCP/S clients that implement :nack do so with modack(0).

So I could get by with :ack and :nack as options, provided I could send an integer as the config value:

Broadway.Message.configure_ack(message, nack: 600)

Thoughts?

[josevalim]

We will call the configure callback, which means all options are up to you. However we will probably standardize on a convention for on_success/on_failure/on_error so users can customize when acking happens. For example, I can see some users wanting to ack on expected failure cases. -- *José Valimwww.plataformatec.com.br <http://www.plataformatec.com.br/>Founder and Director of R&D*

[mcrumm]

For example, I can see some users wanting to ack on expected failure cases.

I'm certain this will be the case, especially for GCP/S consumers, as the only way to remove a message from the queue is to acknowledge it.

[whatyouhide]

Closed by #109.