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.

まず、Routed Dynamic virtual-router 実装を使用する Isolated ネットワークを追跡し、keepalived を使用する natted virtual-router 実装と比較します。完了条件は、active/passive virtual-router が冗長性を提供し、ホストまたは VM の障害によってデフォルトゲートウェイ、DHCP、DNS、またはネットワークが中断されないことです。

索引モデルが issue の本文から書いたものです。