feat: add support for security group referencing to transit-gateway module

AWS recently introduced security group referencing for Transit Gateway VPC attachments. This feature was available in the standalone resource `aws_ec2_transit_gateway_vpc_attachment` but not in the transit-gateway module. Added support for it in the module.

Author: syedimranhassan

main.tf

@@ -73,6 +73,7 @@ resource "aws_ec2_transit_gateway_vpc_attachment" "this" {
   dns_support                                     = try(each.value.dns_support, true) ? "enable" : "disable"
   ipv6_support                                    = try(each.value.ipv6_support, false) ? "enable" : "disable"
   appliance_mode_support                          = try(each.value.appliance_mode_support, false) ? "enable" : "disable"
+  security_group_referencing_support              = try(each.value.security_group_referencing_support, false) ? "enable" : "disable"
   transit_gateway_default_route_table_association = try(each.value.transit_gateway_default_route_table_association, true)
   transit_gateway_default_route_table_propagation = try(each.value.transit_gateway_default_route_table_propagation, true)