Ensure permissions are tightly controlled for AWS ElasticSearch Domains

AWS ElasticSearchDomain with sensitive permissions may lead to unauthorized access and/or data leak.

AWS OpenSearch (formerly ElasticSearch) can be configured to use IAM policies similar to most other Amazon services. To learn more about how to configure IAM policies to use with OpenSearch, see the AWS documentation (below).

In Terraform -

1. In the aws_elasticsearch_domain resource, set the access_policies field with the IAM policy accordingly.

References:
https://docs.aws.amazon.com/opensearch-service/latest/developerguide/ac-managed.html
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/elasticsearch_domain