provide function castAsEndPoint to hook justpy webpage returning function as Starlette endpoint

[sandeep-gh]

CastAsEndpoint would provide a wrapper around justpy endpoint function (which returns a webpage class) to create a function
that returns a Starlette response. The function would act as endpoint for the provided pathglob.

[WolfgangFahl]

We already have a decorator "reponse" for this now.

[WolfgangFahl]

@jp.app.route("/greet/{name}")
@jp.app.response
def greeting_function(request):
    wp = jp.WebPage()
    name = f"""{request.path_params["name"]}"""
    wp.add(jp.P(text=f"Hello there, {name}!", classes="text-5xl m-2"))
    return wp

@jp.app.jproute("/bye")
def bye_function(_request):
    wp = jp.WebPage()
    wp.add(jp.P(text="Bye bye!", classes="text-5xl m-2"))
    return wp

the next step will be to make the legacy SetRoute work again as per #502