Support for jetstream publish confirmation

[awoimbee]

From the docs:

If you want to persist your messages you can do a normal publish to the subject for unacknowledged delivery, though it's better to use the JetStream context publish calls instead as the JetStream server will reply with an acknowledgement that it was successfully stored.

AFAIK this library implements only the normal publish with unacknowledged delivery (Gnat.pub/4).
There should be a function Gnat.JetStream.pub/4.

[mmmries]

@awoimbee I think you can just swap Gnat.pub with Gnat.request which will wait for a reply form the stream to confirm it has persisted your message.

Perhaps we should add a named function just to make it easier to find the right function in the docs?

[awoimbee]

Thanks, it works great! It returns this:

{:ok, %{
   gnat: #PID<0.2440.0>,
   body: "{\"stream\":\"MY_STREAM\",\"seq\":920}",
   topic: "_INBOX.KrIxGq56ZCr4F6b8.MQsTo1ZZJmJRNR3U",
   reply_to: nil
}}

---

Yeah it would be nice to have a simple function that could BTW check that the response indeed comes from jetstream, like the python client does

[mmmries]

Yep, we should at least document that in the gnat documentation to make it easy to find, or just add a function with a more specific name so people can find it. Consider it on the TODO list for this project. Any PRs welcome if someone else wants to beat me to it