Netris: fix UnsupportedOperationException when create VPC offering with NATTED mode (#75)

fixes
```
2025-03-21T10:42:55,039 ERROR [c.c.a.ApiServer] (qtp1513608173-21:[ctx-f9c7f002, ctx-bcfe846d]) (logid:e12e798f) unhandled exception executing api command: [Ljava.lang.String;@3a1416cd java.lang.UnsupportedOperationException
        at java.base/java.util.AbstractList.add(AbstractList.java:153)
        at java.base/java.util.AbstractList.add(AbstractList.java:111)
        at org.apache.cloudstack.api.command.admin.vpc.CreateVPCOfferingCmd.getServiceProviderMapForExternalProvider(CreateVPCOfferingCmd.java:248)
```

Author: weizhouapache

api/src/main/java/org/apache/cloudstack/api/command/admin/vpc/CreateVPCOfferingCmd.java

@@ -243,7 +243,7 @@ public Map<String, List<String>> getServiceProviders() {
     }
 
     private void getServiceProviderMapForExternalProvider(Map<String, List<String>> serviceProviderMap, String provider) {
-        List<String> unsupportedServices = Arrays.asList("Vpn", "BaremetalPxeService", "SecurityGroup", "Connectivity", "Firewall");
+        List<String> unsupportedServices = new ArrayList<>(List.of("Vpn", "BaremetalPxeService", "SecurityGroup", "Connectivity", "Firewall"));
         if (NetworkOffering.NetworkMode.NATTED.name().equalsIgnoreCase(getNetworkMode())) {
             unsupportedServices.add("Gateway");
         }