HTTP / ECS credential provider (IAM Roles for Tasks) (#765)

* Add HTTP provider base

* add retry logic and tests

* Add support for authorization headers

* Fix clippy & docs failures

This commit also fixes aws/sdk/build.gradle.kts to exclude node modules.

* fix smithy-client

* Apply suggestions from code review

Co-authored-by: Zelda Hessler <zelda.hessler@pm.me>
Co-authored-by: John DiSanti <jdisanti@amazon.com>

* CR feedback and cleanups

* update changelog