VPC now supports private IPv6 via IPAM

[mkarakas]

Describe the problem
A clear and concise description of what is wrong with the documentation.

As of August 2024, VPCs now support private IPv6/ULA addresses with IPAM: https://aws.amazon.com/about-aws/whats-new/2024/08/aws-private-ipv6-addressing-vpcs-subnets/

As such below should be reworked:

"VPCs do not support assigning private IPv6 addresses from the Unique Local Address (ULA) range as defined by RFC 4193 (fd00::/8 or fc00::/8). This is true even when you would like to assign an IPv6 CIDR owned by you. Egressing to the internet from Private Subnets is supported by implementing an egress-only internet gateway (EIGW) in a VPC, allowing outbound traffic while blocking all incoming traffic."

References
https://aws.github.io/aws-eks-best-practices/networking/ipv6/

[dumlutimuralp]

@Tim-AWS you can assign this issue to me. I will be working on it.