fix(elasticloadbalancingv2): open, dual-stack-without-public-ipv4 ALB…

… does not allow IPv6 inbound traffic (under feature flag) (#32765)

### Issue # (if applicable)

Closes #32197 .

### Reason for this change

Default generated security group ingress rules for open, dual-stack-without-public-ipv4 ALB does not allow IPv6 traffic. Only a rule for IPv4 ingress traffic is added to the security group rules currently.

### Description of changes

Introduced a new feature flag which is enabled by default so that default generated security group ingress rules now have an additional rule that allows IPv6 ingress from anywhere. 


### Describe any new or updated permissions being added

No new IAM permissions. Added IPv6 security group ingress rules for open, internet-facing ALBs if IP address type  is `dual-stack-without-public-ipv4` and feature flag is set to `true` (default).


### Description of how you validated changes

Added unit test which checks the security group rules for both cases where feature flag is enabled/disabled. Updated integration test snapshot.

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

Co-authored-by: Clare Liguori <clareliguori@users.noreply.github.com>

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk-testing/framework-integ/test/aws-elasticloadbalancingv2/test/integ.alb.dualstack-without-public-ipv4.js.snapshot/aws-cdk-elbv2-integ-dualstack-without-public-ipv4.template.json

@@ -530,6 +530,13 @@
       "FromPort": 80,
       "IpProtocol": "tcp",
       "ToPort": 80
+     },
+     {
+      "CidrIpv6": "::/0",
+      "Description": "Allow from anyone on port 80",
+      "FromPort": 80,
+      "IpProtocol": "tcp",
+      "ToPort": 80
      }
     ],
     "VpcId": {