Add support for writing to the response body stream

[mauroservienti]

A request kicks off a composition process to gather information from various sources. This information is then rendered into a PDF file that needs to be streamed back to the response.

ServiceComposer makes the above scenario very hard to implement because it always assumes to own the response, and then, before writing to the body, it tries to serialize the view model.

[mauroservienti]

An option is available today: Enable output formatters support in ServiceComposer and then use an MVC ActionResult to return a FileStreamResult. This test validates it works as intended:

ServiceComposer.AspNetCore/src/ServiceComposer.AspNetCore.Tests/Get_with_2_handlers_output_formatter_file_stream_result.cs

Lines 18 to 32 in bbb7dfb

	class TestGetStringHandler : ICompositionRequestsHandler
	{
	[HttpGet("/sample/using-body-stream")]
	public Task Handle(HttpRequest request)
	{
	var buffer = Encoding.UTF8.GetBytes(expected_string_content);
	request.SetActionResult(new FileStreamResult
	(
	new MemoryStream(buffer),
	"text/plain"
	));
	return Task.CompletedTask;
	}
	}

[mauroservienti]

Another option could be to allow plugging in different serializers other than the default one that assumes the response ca be json serialized. Ideally, serializers should be route-bound.