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_

Riprodurre il problema in CloudStack 4.20.0.0 creando un gateway privato, aggiungendo un Destination Network CIDR e inviandone un secondo tramite il controllo «Add route». Tracciare l’entry point per l’aggiunta delle route del private gateway e verificare che vengano accettate più route e che il secondo CIDR venga persistito o segnalato con un errore visibile.

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