Provide correct default for Federation Upstream "MessageTTL"

[StateOfDenial]

Environment

Go version: 1.19
Rabbithole version: v2.12.0
RabbitMQ version: 3.10.2

Issue

According to the RabbitMQ documentation, when creating an exchange federation upstream the default value for Message TTL is none, or blank. However when I don't set the MessageTTL value for an API call (see code example), the library sets the value to 0 which has a different meaning and I can not intentionally pass in a blank value.

Expected behaviour

The ability to pass in an explicit empty value and for the default value to be empty.

Code example

package main

import (
    "github.com/michaelklishin/rabbit-hole/v2"
)

func main() {
    rmqc, _ := rabbithole.NewClient("http://rabbitmq.rabbitmq-poc.internal:15672/rabbitmq", "****", "****")
    ups, _ := rmqc.ListFederationUpstreams()
    fmt.Println(ups)

    rmqc.PutFederationUpstream("/", "test", rabbithole.FederationDefinition{
        Uri: rabbithole.URISet{"amqp://vm-cluster.rabbitmq-poc.internal"},
        ReconnectDelay: 3245024,
        AckMode: "on-confirm",
        TrustUserId: false,
        Exchange: "toCloud2",
    })

[michaelklishin]

This is very likely just the behavior of the JSON serialisation. You are welcome to submit a PR.

[ahmadalli]

@michaelklishin Has this been released? I'm still having the same situation on v2.12.0
Thanks for releasing it 👍