OCPBUGS-11796: azure: skip NSG creation when BYO vnet

In an install where users bring their networks they also bring their own
NSGs. However, the installer still creates NSG. In Azure environments
using the rule [1] below, users are prohibited from installing cluster,
as the apiserver_in rule has the rule set as 0.0.0.0. Having a rule in
place where the users could define this before install would allow them
to set this connectivity without having the inbound access.

[1] - Rule: Network Security Groups shall not allow rule with 0.0.0.0/Any Source/Destination IP Addresses - Custom Deny

Author: r4f4

data/data/azure/vnet/nsg.tf

@@ -20,6 +20,7 @@ resource "azurerm_subnet_network_security_group_association" "worker" {
 }
 
 resource "azurerm_network_security_rule" "apiserver_in" {
+  count                       = var.azure_preexisting_network ? 0 : 1
   name                        = "apiserver_in"
   priority                    = 101
   direction                   = "Inbound"