This PR enables Shadowsocks-over-WebSockets functionality in the Caddy server, allowing clients to connect to Shadowsocks servers via WebSockets. This is achieved by introducing three new modules:

1. Named Connection Handlers: These reusable handlers can be shared by different applications and are configured within the Outline app.

2. WebSocket-to-Outline Handler: An HTTP app handler which bridges WebSocket requests to a designated named connection handler, enabling Shadowsocks connections over WebSockets.

3. Layer4 Outline Handler: A layer 4 handler which bridges TCP/UDP connections to a designated named connection handler.

Example Configuration:

This example demonstrates how to configure a Shadowsocks handler with access keys and utilize it for both WebSocket and TCP connections:

  outline:
    ...
    connection_handlers:
    - name: ss1
      handle:
        handler: shadowsocks
        keys:
        - id: user-0
          cipher: chacha20-ietf-poly1305
          secret: Secret0

apps:
  http:
    servers:
      '1':
        listen:
        - ":8000"
        routes:
        - match:
          - path:
            - "/tcp"
          handle:
          - handler: websocket2layer4
            type: stream
            connection_handler: ss1
  layer4:
    servers:
      '1':
        listen:
        - tcp/[::]:9000
        routes:
        - handle:
          - handler: outline
            connection_handler: ss1