Redundant Virtual Router support in Isolated network with network mode set to Routed Dynamic

### Feature request

At the moment, the _Isolated network with Routed Dynamic network mode_ only supports running with a single virtual router. This means in the event of a host or VM failure, there will be a network outache of about 5 to 7 minutes. This virtual router is the default gateway of all VM's in this network, so the impact can mean downtime and loss of services (DHCP, DNS, networking).

### Solution

It would be great to have the same implementation as the "natted" virtual router type where keepalived is used between an active and passive virtual router in order to give redundancy.

Inizia tracciando la rete Isolated con l’implementazione Routed Dynamic virtual-router e confrontandola con l’implementazione natted virtual-router che utilizza keepalived. Il lavoro è completato quando virtual-router attivi/passivi forniscono ridondanza, in modo che un guasto dell’host o della VM non interrompa il gateway predefinito, DHCP, DNS o la rete.

Scritto dal modello di indicizzazione a partire dal testo della issue.