Migrate http1 proxy connect handler (#185)

Motivation:

Moving the HTTP1ProxyConnectHandler into swift-nio-extras will make the
code which is generally useful when dealing with HTTP1 proxies available
more easily to a wider audience.

Modifications:

The code and tests are copied over from https://github.com/swift-server/async-http-client/blob/0b5bec741bfcf941e208d937de2ec29affe750a7/Sources/AsyncHTTPClient/ConnectionPool/ChannelHandler/HTTP1ProxyConnectHandler.swift.

Result:

HTTP1ProxyConnectHandler will be surfaced via the NIOExtras library

NOTICE.txt

@@ -32,3 +32,14 @@ This product contains a derivation of the Tony Stone's 'process_test_files.rb'.
     * https://www.apache.org/licenses/LICENSE-2.0
   * HOMEPAGE:
     * https://codegists.com/snippet/ruby/generate_xctest_linux_runnerrb_tonystone_ruby
+
+---
+
+This product contains a derivation of "HTTP1ProxyConnectHandler.swift" and accompanying tests from AsyncHTTPClient.
+
+  * LICENSE (Apache License 2.0):
+    * https://www.apache.org/licenses/LICENSE-2.0
+  * HOMEPAGE:
+    * https://github.com/swift-server/async-http-client
+
+---

Package.swift

@@ -21,6 +21,7 @@ var targets: [PackageDescription.Target] = [
         dependencies: [
             .product(name: "NIO", package: "swift-nio"),
             .product(name: "NIOCore", package: "swift-nio"),
+            .product(name: "NIOHTTP1", package: "swift-nio"),
         ]),
     .target(
         name: "NIOHTTPCompression",

Package@swift-5.5.swift

@@ -21,6 +21,7 @@ var targets: [PackageDescription.Target] = [
         dependencies: [
             .product(name: "NIO", package: "swift-nio"),
             .product(name: "NIOCore", package: "swift-nio"),
+            .product(name: "NIOHTTP1", package: "swift-nio")
         ]),
     .target(
         name: "NIOHTTPCompression",