[tests] implement 1.4.4 (10.4) IPv4 built-in NAT64 connectivity test

This commit implements the 10.4 [1.4] [CERT] IPv4 Connectivity using
BR built-in NAT64 integration test.

It includes:
- Modifying test_dind_dns_sd.sh to configure the infrastructure-link
  Docker network with an IPv4 subnet (192.168.1.0/24) to support
  static IP assignments, and registering the new expect test.
- Creating expect script tests/scripts/expect/dind_1_4_pic_tc_4.exp
  that spins up a simulated internet host (eth2-server) and local
  host (eth1-server), configures static routing, verifies NAT64
  prefix discovery, resolves DNS queries dynamically with DNS64,
  and tests ICMPv6/UDP ping and HTTP GET bidirectional communication.

Author: jwhui