[EKS] [request]: Support for creating managed node group without public IPv4 addresses in public subnets

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**Tell us about your request**
This is a request that managed node group in public subnets can be created if IPv6 addresses are assigned and public IPv4 addresses aren't assigned.
Currently, when creating managed node group in public subnets, assigning public IPv4 addresses is necessary.

**Which service(s) is this request for?**
EKS

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
When attempting to create a managed node group in public subnets with ```MapPublicIpOnLaunch: false``` and ```AssignIpv6AddressOnCreation: true```, the following error occurs.
```
Ec2SubnetInvalidConfiguration - One or more Amazon EC2 Subnets of [subnet-xxx, subnet-xxx] for node group xxx does not automatically assign public IP addresses to instances launched into it. If you want your instances to be assigned a public IP address, then you need to enable auto-assign public IP address for the subnet. See IP addressing in VPC guide: https://docs.aws.amazon.com/vpc/latest/userguide/vpc-ip-addressing.html#subnet-public-ip
```

Therefore, nodes that have IPv6 addresses but do not have public IPv4 addresses in public subnets cannot be created.

**Are you currently working around this issue?**
self-managed nodes

**Additional context**
N/A

**Attachments**
N/A

No repository files, tests, or entry points are named. Start by reviewing the EKS managed node group behavior described with MapPublicIpOnLaunch=false and AssignIpv6AddressOnCreation=true; done means public-subnet managed node groups can use IPv6 without public IPv4 addresses and no longer produce the reported error.

Written by the indexing model from the issue text.