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)

実装ファイルやテストは指定されていません。まず、一覧にある network-offering と isolated-network の手順で失敗を再現し、次に関連するディスカッション #13052 を読み、パブリック IP の取得に関するバリデーションを追跡してください。完了の条件は、既存の Source NAT の動作を壊すことなく、Static NAT を使用し、Source NAT を使用しない高度な分離ネットワークにパブリック IP を追加できることです。

索引モデルが issue の本文から書いたものです。