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/utils/rand.go

@@ -0,0 +1,29 @@
+package utils
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+)
+
+// Rand is a wrapper around crypto/rand that adds some convenience functions known from math/rand.
+type Rand struct {
+	buf [4]byte
+}
+
+func (r *Rand) Int31() int32 {
+	rand.Read(r.buf[:])
+	return int32(binary.BigEndian.Uint32(r.buf[:]) & ^uint32(1<<31))
+}
+
+// copied from the standard library math/rand implementation of Int63n
+func (r *Rand) Int31n(n int32) int32 {
+	if n&(n-1) == 0 { // n is power of two, can mask
+		return r.Int31() & (n - 1)
+	}
+	max := int32((1 << 31) - 1 - (1<<31)%uint32(n))
+	v := r.Int31()
+	for v > max {
+		v = r.Int31()
+	}
+	return v % n
+}