docs(s2n-tls-hyper): Add hyper client/server example

[goatgoose]

Resolved issues:

Addresses #5000 (review)

Description of changes:

Adds a client and server example for using s2n-tls with hyper. The example client sends an HTTP request to the server, and the server echos the request body back the client in its response.

Call-outs:

Let me know if I can make anything in the examples more clear!

Testing:

The client/server examples will be built in CI. I ran them locally to make sure they work.

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

[lrstewart]

Nit, mostly curious: Why 1142? I'm not sure that's a random choice I've seen before

[goatgoose]

It's the last part of my phone number :D

[lrstewart]

Could I run the client without the server? Like cargo run --bin client -- --addr "google.com"?

Right now I think it'd fail because of no echo, but should it maybe just print the response or something instead or asserting the response?

[goatgoose]

Yes, it'd work on other servers too! That makes sense, I'll remove the assertion.

[goatgoose]

I confirmed that it works by testing amazon.com. 🤔

❯ cargo run --bin client -- --addr www.amazon.com
...
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[lrstewart]

I remember this was discussed in a previous PR. So we landed on manually setting the alpn via s2n-tls? Idk, this example might make me rethink that choice :/

[goatgoose]

The ALPN doesn't need to be manually configured with s2n-tls-hyper. It will attempt to negotiate HTTP/2 by automatically setting the ALPN:

s2n-tls/bindings/rust/standard/s2n-tls-hyper/src/connector.rs

Lines 186 to 200 in 3e57b05

	// Attempt to negotiate HTTP/2 by including it in the ALPN extension. Other supported HTTP
	// versions are also included to prevent the server from rejecting the TLS connection if
	// HTTP/2 isn't supported:
	//
	// https://datatracker.ietf.org/doc/html/rfc7301#section-3.2
	// In the event that the server supports no
	// protocols that the client advertises, then the server SHALL respond
	// with a fatal "no_application_protocol" alert.
	let builder = connection::ModifiedBuilder::new(self.conn_builder.clone(), |conn| {
	conn.set_application_protocol_preference([
	b"h2".to_vec(),
	b"http/1.1".to_vec(),
	b"http/1.0".to_vec(),
	])
	});

This is a hyper server example which directly uses s2n-tls-tokio, not s2n-tls-hyper. s2n-tls-hyper is only used with the hyper client.