feat: Update customWebName and virtualNetwork modules

Bug fix: The code changes in the `customWebName.bicep` module update the `subdomain` parameter to use the `subdomain` variable instead of a hardcoded value. This change allows for more flexibility in configuring the subdomain for the custom web name, whilst fixing a bug because the full fqdn was used by mistake.

Bug fix: In the `virtualNetwork.bicep` module, the `natGateway` property under `gatewaySubnetName` has been removed. This change removes the dependency on a NAT gateway for the gateway subnet that prevented its deployment.

These updates improve the configuration and flexibility of the OCPP server infrastructure.

ocpp-server/infra/modules/customWebName.bicep

@@ -29,7 +29,7 @@ module verification 'dnstxt.bicep' = {
   scope: resourceGroup(dnsZoneRG)
   params: {
     dnszoneName: dnszoneName
-    subdomain: 'asuid.${fqdn}'
+    subdomain: 'asuid.${subdomain}'
     value: site.properties.customDomainVerificationId
   }
 }

ocpp-server/infra/modules/virtualNetwork.bicep

@@ -46,9 +46,6 @@ resource virtualNetwork 'Microsoft.Network/virtualNetworks@2019-09-01' = {
       {
         name: gatewaySubnetName
         properties: {
-          natGateway: {
-            id: natGatewayId
-          }
           addressPrefix: gatewaySubnetPrefix
         }
       }