Rethink the setters paradigm

[xibz]

Setters are not heavily used in Go, so we should revisit a more idiomatic approach either by setting things on the struct directly or using functions options which is pretty standard in Go

So instead of

event := cdevents.NewSomeCDEvent()
event.SetFoo("foo")

we'd have something more like

event := cdevents.NewSomeCDEvent(cdevent.SomeCDEventOptions.WithFields(func(e cdevents.SomeCDEvent) {
    e.Foo = "foo"
})

// or
event := cdevents.NewSomeCDEvent(cdevent.SomeCDEventOptions.WithFoo("foo"))

Or a combination of the two. So is one better than the other? Not necessarily. But one is more idiomatic, and that's crucial for SDKs.