TUN-4597: Add a QUIC server skeleton

- Added a QUIC server to accept streams
- Unit test for this server also tests ALPN
- Temporary echo capability for HTTP ConnectionType

vendor/github.com/lucas-clemente/quic-go/internal/protocol/encryption_level.go

@@ -0,0 +1,30 @@
+package protocol
+
+// EncryptionLevel is the encryption level
+// Default value is Unencrypted
+type EncryptionLevel uint8
+
+const (
+	// EncryptionInitial is the Initial encryption level
+	EncryptionInitial EncryptionLevel = 1 + iota
+	// EncryptionHandshake is the Handshake encryption level
+	EncryptionHandshake
+	// Encryption0RTT is the 0-RTT encryption level
+	Encryption0RTT
+	// Encryption1RTT is the 1-RTT encryption level
+	Encryption1RTT
+)
+
+func (e EncryptionLevel) String() string {
+	switch e {
+	case EncryptionInitial:
+		return "Initial"
+	case EncryptionHandshake:
+		return "Handshake"
+	case Encryption0RTT:
+		return "0-RTT"
+	case Encryption1RTT:
+		return "1-RTT"
+	}
+	return "unknown"
+}