Add-AzKeyVaultNetworkRule adds duplicated IPs

### Description

Add-AzKeyVaultNetworkRule adds duplicated IPs into the firewall rule while Azure portal doesn't allow IP overlap, can you please enable the overlap IP check in Add-AzKeyVaultNetworkRule.

### Issue script & Debug output

```PowerShell
After the duplicate IPs added into the AKV firewall rule by Add-AzKeyVaultNetworkRule, I got some problem to cleanup the duplicated IPs from azure portal as well, the IPs cannot be removed even it tells the change applied successfully.
```

### Environment data

```PowerShell
n/a
```

### Module versions

```PowerShell
n/a
```

### Error output

```PowerShell
n/a
```

Start at Add-AzKeyVaultNetworkRule and trace how it handles network-rule IPs and validation. Reproduce the duplicate-IP scenario described in the issue, then verify that overlapping IPs are rejected consistently with the Azure portal and that the resulting firewall rule does not contain duplicates.

Written by the indexing model from the issue text.