*breaking change*: Refactor httpLabel behavior around optionality (#537)

* *breaking change*: Refactor httpLabel behavior around optionality

**This change is breaking because fields with the `httpLabel` go from `T` to `Option<T>` in generated models.**

Previously, existence of `httpLabel` would cause a non-optional field to be generated. But:
1. This is wrong. Protocols should not impact models.
2. This causes issues when generating the transcribe service because the `httpLabel` trait is attached to the model.
3. This leads to a bad user experience of the field is unset—A default value is inserted but that leads to a signing error down the line.

This change will cause a failure during request construction if fields targetted with `httpLabel` are either unset or empty.

An integration test validating this behavior for S3 was also added.

* Remove unused container parameter

* Ignore clippy another clippy lint

* Fix clippy lint name