`Peer`: how to connect to upstream

In the upstream_peer() phase the user should return a Peer object which defines how to connect to a certain upstream.

`Peer`

A HttpPeer defines which upstream to connect to.

attribute	meaning
address: `SocketAddr`	The IP:Port to connect to
scheme: `Scheme`	Http or Https
sni: `String`	The SNI to use, Https only
proxy: `Option<Proxy>`	The setting to proxy the request through a CONNECT proxy (opens in a new tab)
client_cert_key: `Option<Arc<CertKey>>`	The client certificate to use in mTLS connections to upstream
options: `PeerOptions`	See below

`PeerOptions`

A PeerOptions defines how to connect to the upstream.

attribute	meaning
bind_to: `Option<InetSocketAddr>`	Which local address to bind to as the client IP
connection_timeout: `Option<Duration>`	How long to wait before giving up establishing a TCP connection
total_connection_timeout: `Option<Duration>`	How long to wait before giving up establishing a connection including TLS handshake time
read_timeout: `Option<Duration>`	How long to wait before each individual `read()` from upstream. The timer is reset after each `read()`
idle_timeout: `Option<Duration>`	How long to wait before closing a idle connection waiting for connection reuse
write_timeout: `Option<Duration>`	How long to wait before a `write()` to upstream finishes
verify_cert: `bool`	Whether to check if upstream' server cert is valid and validated
verify_hostname: `bool`	Whether to check if upstream server cert's CN matches the SNI
alternative_cn: `Option<String>`	Accept the cert if the CN matches this name
alpn: `ALPN`	Which HTTP protocol to advertise during ALPN, http1.1 and/or http2
ca: `Option<Arc<Box<[X509]>>>`	Which Root CA to use to validate the server's cert
tcp_keepalive: `Option<TcpKeepalive>`	TCP keepalive settings to upstream

Examples

TBD