Add support for processing HtmxResponse in the Model and as an Argument

[checketts]

Addresses #127

This enables the following usecase:

@GetMapping("/admin")
fun getAdmin(htmxResponse: HtmxResponse.Builder): JteModel {
    htmxResponse.trigger("aTrigger")
    return templates.adminIndex("Hello")
}

The JteModel is a typed template. But the HtmxResponse can be used as an argument to inform any triggers, redirect, etc. that need to happen.

This change also supports adding HtmxReponse to the model and being processed, if that approach is needed.

[wimdeblauwe]

Can you add some documentation to the README on how to use this?

[checketts]

I've added the readme examples.