feat: Add NAT gateway interface ids output (#1006)

* feat: Output network interface IDs of NAT gateways

* docs: updated README

---------
Co-authored-by: Bryant Biggs <bryantbiggs@gmail.com>

README.md

@@ -637,6 +637,7 @@ No modules.
 | <a name="output_nat_ids"></a> [nat\_ids](#output\_nat\_ids) | List of allocation ID of Elastic IPs created for AWS NAT Gateway |
 | <a name="output_nat_public_ips"></a> [nat\_public\_ips](#output\_nat\_public\_ips) | List of public Elastic IPs created for AWS NAT Gateway |
 | <a name="output_natgw_ids"></a> [natgw\_ids](#output\_natgw\_ids) | List of NAT Gateway IDs |
+| <a name="output_natgw_interface_ids"></a> [natgw\_interface\_ids](#output\_natgw\_interface\_ids) | List of Network Interface IDs assigned to NAT Gateways |
 | <a name="output_outpost_network_acl_arn"></a> [outpost\_network\_acl\_arn](#output\_outpost\_network\_acl\_arn) | ARN of the outpost network ACL |
 | <a name="output_outpost_network_acl_id"></a> [outpost\_network\_acl\_id](#output\_outpost\_network\_acl\_id) | ID of the outpost network ACL |
 | <a name="output_outpost_subnet_arns"></a> [outpost\_subnet\_arns](#output\_outpost\_subnet\_arns) | List of ARNs of outpost subnets |

outputs.tf

@@ -484,6 +484,11 @@ output "natgw_ids" {
   value       = aws_nat_gateway.this[*].id
 }
 
+output "natgw_interface_ids" {
+  description = "List of Network Interface IDs assigned to NAT Gateways"
+  value       = aws_nat_gateway.this[*].network_interface_id
+}
+
 ################################################################################
 # Egress Only Gateway
 ################################################################################