New Resource: aws_lightsail_domain_entry

[loivis]

lightsail domain entry for #2731

This is my first attempt to implement a new resource. Comments and feedbacks are welcome.

The resource is at least working for now. But I do have a few questions about the implementation.

1. The resource schema follows the same schema as AWS API for CreateDomainEntryInput,
   UpdateDomainEntryInput, DeleteDomainEntryInput. I'm not sure if it's good idea to flat all into common TypeString. In that case, it will make the implementation a bit easier but break the identical mapping between terraform and AWS API.

2. Name for the domain entry in AWS API is the full FQDN with domain name. From user perspective, it would be easier to just use a string without domain name. We can append domain name before sending request to AWS. The same concern of identical mapping applies here as well. Still I'm following convention for AWS API.

3. In AWS API DomainEntry, options is already marked as Deprecated. So I didn't add this parameter at all.

4. I haven't fully figured out how import works, so support for import is not there yet.

5. I'd like to validate target argument based on is_alias. AFAIK, ValidateFunc works only for the current argument. I don't have it in mind where similar logic is implemented.

[loivis]

I won't be able to continue the work so close it.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!