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.

Start by tracing the Isolated network with Routed Dynamic virtual-router implementation and comparing it with the natted virtual-router implementation that uses keepalived. Done means active/passive virtual routers provide redundancy so a host or VM failure does not interrupt the default gateway, DHCP, DNS, or networking.

Written by the indexing model from the issue text.