Allow public IP acquisition without Source NAT

Allow public IP acquisition without Source NAT in Isolated Networks with Static NAT

ISSUE TYPE
- Improvement Request

COMPONENT NAME
```
```
CLOUDSTACK VERSION
```
4.20.3
```
SUMMARY

In an isolated network without Source NAT, it is not possible to add a public IP address when Static NAT is enabled.

Error:
```
Failed to acquire IP.
In zone of type Advanced ip address can be associated only to the network of guest type Isolated with the SourceNat enabled
```

It would be useful to have this capability, since Source NAT reserves a separate public IP address for itself. In scenarios where all VMs are expected to use Static NAT, the Source NAT IP remains idle and unused.

STEPS TO REPRODUCE
1) Create network offering for guest isolated network
2) Enable Static NAT in the offering
4) Create an isolated network using the created offering
5) Add a public IP address

Related discussion: [Error when adding a public IP in an isolated network without Source NAT (using Static NAT) #13052](https://github.com/apache/cloudstack/discussions/13052)

Non sono indicati file di implementazione né test. Inizia riproducendo il problema seguendo i passaggi elencati per network-offering e isolated-network, quindi leggi la discussione correlata #13052 e traccia la validazione dell’acquisizione dell’IP pubblico. Il lavoro è completato quando è possibile aggiungere un IP pubblico a una rete isolata avanzata con Static NAT e senza Source NAT, senza compromettere il comportamento esistente di Source NAT.

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