sse example using datastar

The current example has hard coded js at https://github.com/goadesign/examples/blob/master/sse/public/index.html

Suggest we look at using datastar because it removes all custom JS, by using a htmx pattern: https://github.com/starfederation/datastar/tree/develop/examples/go/hello-world

```sh

go run .

```

The Goa DSL is designed around the notion oF resources and so is datastar. So I think code gen will work really well with it. also they both use Chi.

it makes it possible to essentially gen some of the GUI, because all state is on the server and simple HTML fragments are all that is needed. tailwind css is all there as you can see from the HTML.