MNHA: Dual stacking of IPv4 and IPv6 addresses for hybrid and switching modes

We support dual-stack (IPv4 and IPv6) addresses for virtual IP for Multinode High Availability (MNHA) operating in default gateway mode or hybrid mode. The virtual-ip configuration under the [edit chassis high-availability services-redundancy-group] hierarchy is extended to accept a list of IP addresses, allowing both IPv4 and IPv6 virtual IP address configuration on the same interface.

MNHA uses both address families to detect and resolve split brain conditions. If either address family is reachable, the probe succeeds and the services redundancy group state machine responds accordingly. This support improves MNHA adoption in dual stack environments.