Multiple static routes inside one private gateway.

### problem

As an admin I want to have possibility to add more than one static route to private gateway.
Unfortunately, I'm not sure if this a bug or a feature.

But if I try to add the second static route (Destination Network CIDR) to Private Gateway, just nothing happens after I push the "Add route" button. Screenshot with example is attached.


### versions

The versions of ACS, hypervisors, storage, network etc..
Current ACS version is 4.20.0.0
Previous vith the same issue: 4.19.1
Hypervisors: XCP-NG 8.2.1

### The steps to reproduce the bug

1. Create new Private Pateway
2. Add first Destination Network CIDR
3. Add second Destination Network CIDR

### What to do about it?

_No response_

在 CloudStack 4.20.0.0 中重现该问题：创建一个私有网关，添加一个 Destination Network CIDR，然后通过“Add route”控件提交第二个 CIDR。跟踪私有网关的路由添加入口点，并验证是否接受多条路由，以及第二个 CIDR 是否已持久化，或是否报告了可见错误。

由索引模型根据 Issue 内容生成。