Test `httpRequestTests` against actual Services (#1708)

* Make Instantiator generate default values for required field on demand

* Move looping over operations into ServerProtocolTestGenerator

Signed-off-by: Weihang Lo <weihanglo@users.noreply.github.com>

* Add protocol test helper functions

Signed-off-by: Weihang Lo <weihanglo@users.noreply.github.com>

* Add method param to construct http request

* Put request validation logic inside closure

Signed-off-by: Weihang Lo <weihanglo@users.noreply.github.com>

* Make protocol test response instantiate with default values

* Add module meta for helper module

Signed-off-by: Weihang Lo <weihanglo@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: david-perez <d@vidp.dev>

* Address most style suggestions

* add companion object for attribute #[allow(dead_code)]

Signed-off-by: Weihang Lo <weihanglo@users.noreply.github.com>

* Use writable to make code readable

* recursively call `filldefaultValue`

Signed-off-by: Weihang Lo <weihanglo@users.noreply.github.com>

* Exercise with `OperationExtension`

* Temporary protocol tests fix for awslabs/smithy#1391

Missing `X-Amz-Target` in response header

* Add `X-Amz-Target` for common models

Signed-off-by: Weihang Lo <weihanglo@users.noreply.github.com>
Co-authored-by: david-perez <d@vidp.dev>
Co-authored-by: Harry Barber <hlbarber@amazon.co.uk>