[feature]: Add aws_external_delegated_zone module

[fullykubed]

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What new functionality would you like to see?

We should have a module for setting up zones for domains registered in non-AWS providers.

How would you use this new functionality?

This would make it easier for users who cannot transfer their domains to AWS accounts for management.

This would not be the default / recommended setup, but would be a valuable escape hatch module to include.