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.

首先追蹤採用 Routed Dynamic virtual-router 實作的 Isolated 網路，並將其與使用 keepalived 的 natted virtual-router 實作進行比較。完成的標準是 active/passive virtual-router 提供備援，使主機或 VM 故障不會中斷預設閘道、DHCP、DNS 或網路。

由索引模型根據 Issue 內容生成。