Add CID send only client example

Adds an example for a client that only sends connection IDs (i.e. does
not request to received them). This is the most common scenario for DTLS
clients.

Signed-off-by: Daniel Mangum <georgedanielmangum@gmail.com>

examples/dial/cid/main.go

@@ -0,0 +1,50 @@
+// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+// Package main implements an example DTLS client using a pre-shared key.
+package main
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"time"
+
+	"github.com/pion/dtls/v2"
+	"github.com/pion/dtls/v2/examples/util"
+)
+
+func main() {
+	// Prepare the IP to connect to
+	addr := &net.UDPAddr{IP: net.ParseIP("127.0.0.1"), Port: 4444}
+
+	//
+	// Everything below is the pion-DTLS API! Thanks for using it ❤️.
+	//
+
+	// Prepare the configuration of the DTLS connection
+	config := &dtls.Config{
+		PSK: func(hint []byte) ([]byte, error) {
+			fmt.Printf("Server's hint: %s \n", hint)
+			return []byte{0xAB, 0xC1, 0x23}, nil
+		},
+		PSKIdentityHint:       []byte("Pion DTLS Server"),
+		CipherSuites:          []dtls.CipherSuiteID{dtls.TLS_PSK_WITH_AES_128_CCM_8},
+		ExtendedMasterSecret:  dtls.RequireExtendedMasterSecret,
+		ConnectionIDGenerator: dtls.OnlySendCIDGenerator(),
+	}
+
+	// Connect to a DTLS server
+	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+	defer cancel()
+	dtlsConn, err := dtls.DialWithContext(ctx, "udp", addr, config)
+	util.Check(err)
+	defer func() {
+		util.Check(dtlsConn.Close())
+	}()
+
+	fmt.Println("Connected; type 'exit' to shutdown gracefully")
+
+	// Simulate a chat session
+	util.Chat(dtlsConn)
+}