Add undocumented ipsec.1-aes256 VPN Connection type

[ewbankkit]

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Closes #23105.

Unable to test the new value, so just ran a simple regression test:

% make testacc TESTS=TestAccEC2VPNConnection_basic PKG=ec2     
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./internal/service/ec2/... -v -count 1 -parallel 20 -run='TestAccEC2VPNConnection_basic'  -timeout 180m
=== RUN   TestAccEC2VPNConnection_basic
=== PAUSE TestAccEC2VPNConnection_basic
=== CONT  TestAccEC2VPNConnection_basic
--- PASS: TestAccEC2VPNConnection_basic (407.05s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/ec2	412.032s

[ketzacoatl]

@ewbankkit If you feel confident enough with your test, I can go with that, but if you need (or prefer) a live test before merge, I'd be happy to do so for you. I'm not familiar with using a custom provider, is there a doc I should read for telling my terraform project to use this branch?

EDIT: I see https://github.com/hashicorp/terraform-provider-aws/blob/main/docs/contributing/development-environment.md#using-the-provider. I don't have golang installed, but will see if I can figure that out and build the provider.

[YakDriver]

I think we give it a go. 🎉

[ewbankkit]

Needs backporting to release/3.x.
Done.

[github-actions]

This functionality has been released in v4.1.0 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]

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