[relay] Feature/relay integration (#2244)

This update adds new relay integration for NetBird clients. The new relay is based on web sockets and listens on a single port.

- Adds new relay implementation with websocket with single port relaying mechanism
- refactor peer connection logic, allowing upgrade and downgrade from/to P2P connection
- peer connections are faster since it connects first to relay and then upgrades to P2P
- maintains compatibility with old clients by not using the new relay
- updates infrastructure scripts with new relay service

encryption/cert.go

@@ -0,0 +1,19 @@
+package encryption
+
+import "crypto/tls"
+
+func LoadTLSConfig(certFile, keyFile string) (*tls.Config, error) {
+	serverCert, err := tls.LoadX509KeyPair(certFile, keyFile)
+	if err != nil {
+		return nil, err
+	}
+
+	config := &tls.Config{
+		Certificates: []tls.Certificate{serverCert},
+		ClientAuth:   tls.NoClientCert,
+		NextProtos: []string{
+			"h2", "http/1.1", // enable HTTP/2
+		},
+	}
+	return config, nil
+}