aws_opensearch_domain support

[Thorleon]

Describe the Feature

aws_opensearch_domain is going to be released soon in aws-provider 4.9.0: hashicorp/terraform-provider-aws#23902 . aws_opensearch_domain is using github.com/aws/aws-sdk-go/service/opensearchservice, which is preferred over github.com/aws/aws-sdk-go/service/elasticsearchservice from aws_elasticsearch_domain.

API operations were replaced with more concise and engine-agnostic names (for example, CreateElasticsearchDomain changed to CreateDomain), but OpenSearch Service continues to support both API versions. For a full list of actions that are no longer supported and their replacements, see the [Configuration API reference for Amazon OpenSearch Service](https://docs.aws.amazon.com/opensearch-service/latest/developerguide/configuration-api.html).

We recommend that you use the new API operations to create and manage domains going forward. Note that when you use the new API operations to create a domain, you need to specify the EngineVersion parameter in the format Elasticsearch_X.Y or OpenSearch_X.Y, rather than just the version number. If you don't specify a version, it defaults to the latest version of OpenSearch.

Source: https://docs.aws.amazon.com/opensearch-service/latest/developerguide/rename.html

Use Case:

Elasticsearch doesn't support XXX.search instance type, see hashicorp/terraform-provider-aws#21787 (comment)

Describe Ideal Solution

Separate repo with feature parity and aws_opensearch_domain implementation. I could take care of writing the code, but it would be awesome if it is released under: https://github.com/cloudposse/.

[cdobbyn]

For others whom may come here, you can upgrade this existing resource to opensearch by changing you version to:
OpenSearch_1.3.

Obviously using the new terraform resource would be ideal, but this doesn't restrict you from updating existing clusters before you're ready to do a terraform state mv once a compatible cloudposse module is available.

Note: I didn't perform the upgrade from Terraform, I did it in the UI and updated Terraform code and state to match the change.

[NemanjaaETF]

Is this module for OSS expected soon to be merged?