add description about http_protocol_ipv6

[shibataka000]

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Summary

This PR add description about http_protocol_ipv6 in aws_launch_template, because #20796 and #21008 added it but didn't update document.

[justinretzolk]

Hey @shibataka000 👋 This looks good to me! Thank you for your contribution!

[github-actions]

This functionality has been released in v3.61.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[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.