Adopt latest AsyncChannel changes (#411)

# Motivation
In my latest PR in NIO, I removed a bunch of API from the bootstrap methods to make the API easier to digest and reduce a number of duplicated code issues.

# Modification
This PR adopts the latest NIO changes and adapts the APIs in H2. More specifically, it removes the `NIOAsyncChannel` convenience methods and makes sure that everything aligns nicely with the proposes bootstrap APIs.

# Result
We now have the APIs in place to bootstrap a protocol negotiated H1/H2 server.

Package.swift

@@ -21,7 +21,7 @@ let package = Package(
         .library(name: "NIOHTTP2", targets: ["NIOHTTP2"]),
     ],
     dependencies: [
-        .package(url: "https://github.com/apple/swift-nio.git", from: "2.56.0"),
+        .package(url: "https://github.com/apple/swift-nio.git", from: "2.57.0"),
         .package(url: "https://github.com/apple/swift-atomics.git", from: "1.0.2"),
         .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0"),
     ],