Add support for new consumer attributes

[mmmries]

According to the NATS Consumer Docs there have been some new attributes added to consumers in nats-server 2.8.3 and 2.10.0.

We should support setting or checking these attributes, but we need to figure out some things like:

• If we attempt to send these attributes to earlier versions of the server, will it fail?
• Should we have different versions of the Consumer struct depending on which versions of the server we're connected to? Or just provide a default value in those new attributes when we lookup consumers from older clusters?

[azabroflovski]

I NEED THIS!!!!! currently I'm using nats-cli directly from code, like this:

def create_consumer(stream, consumer_config) do
  File.write!("/tmp/consumer_[hash].json", consumer_config)

  System.cmd("nats", [
    "consumer",
    "add",
    stream,
    "--config",
    "/tmp/consumer.json"
  ])
end

I'm not a fan of the current approach. Guys who maintain this library could you please either add support for the new fields or make the consumer options more flexible, so that custom options can be passed?

Gnat.Jetstream.API.Consumer.create(:gnat, %Gnat.Jetstream.API.Consumer{
  durable_name: "hui",
  stream_name: "default",
  filter_subject: "test.ab", # This works because it's supported
  filter_subjects: ["subject.example", "another.subject"], # ERROR: Can you enable passing custom options?
  ack_wait: 1,
})

[mmmries]

I've been torn between having structs that fully represent the data model of the jetstream concepts vs having a more "pass through" API. There are some intricacies here with staying backward compatible with older server versions etc. For now I would recommend opening a PR that adds the filter_subjects (or any other new attribute you need to have supported) to this library. It's a relatively straightforward PR to make, but I won't have time in the next couple of days to do it myself.

You can reference #192 for an example of this kind of PR

[mmmries]

You could also work around this by just sending a message to the jetstreap API yourself. The Stream.create functoin is really just a helper around sending a JSON encoded message via the Gnat.request function to the Jetstream API. That might be a lot easier than shelling out to the nats CLI?

[azabroflovski]

@mmmries thanks

[Jarema]

All other clients represents the data model that JetStream actually has.
In recent server version, API Level has been added and it will hopefully make moving forward a bit easier.
As @mmmries said -adding new fields is pretty straightfoward.