Adding IPv6 assign on creation for public subnets

[sc250024]

Allows the user to toggle automatic assignment of IPv6 addresses to public subnets.

Description

Solves issue #185. Basically, this is a mini-feature until #300 is fully approved and merged.

Currently, creation of IPv6 blocks on subnets is a manual process. This makes sure that any of those manual assignments done via the AWS console are not overridden upon running terraform apply.

Motivation and Context

Currently I have public subnets that are assigning IPv6 addresses to instances already, and would like if I could apply Terraform updates without this setting being set to false each time.

Also, I understand that #300 is also using this assign_ipv6_address_on_creation on private / database subnets as well, but as I understand it, this module creates those subnets with the intention to be private-only (i.e. IPv4). Since all IPv6 are publicly routable, I figured it made sense to only put them on public subnets in this PR.

How Has This Been Tested?

• Ran locally against current VPC with public IPv6-enabled subnets.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[secp521]

Can we get some movement on this ?

[sc250024]

@talalatpixlee I think @antonbabenko was on vacation, but he's usually quick about these things. This might not get merged because of #300 existing, but in the end, it's up to him.

[antonbabenko]

As @sc250024 is saying, I am already back from vacation and doing my best to review and release new versions of terraform-aws-modules. Hopefully, I will be able to review #300 and this one during this week.

[antonbabenko]

v2.10.0 has been released (see #317).

[github-actions]

I'm going to lock this pull request because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues. If you have found a problem that seems related to this change, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.