test(s2n-tls-hyper): Add localhost http tests

[goatgoose]

Resolved issues:

Resolves https://github.com/aws/s2n-tls/issues/4631

Description of changes:

This PR adds a way to test s2n-tls-hyper over localhost by using the hyper server to echo HTTP requests back to the s2n-tls hyper client. A few tests were added which make use of the echo framework.

Call-outs:

Now that s2n-tls-hyper is tested locally, the web_client test was removed to reduce flakiness caused by relying on an external endpoint.

Testing:

All tests.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.