[Feature] Add data_stream_options support to elasticstack_elasticsearch_index_template

[maMykola]

Is your feature request related to a problem?

The elasticstack_elasticsearch_index_template resource's template block does not support data_stream_options, which was introduced in Elasticsearch 9.x. This prevents enabling the failure store for data streams via Terraform, requiring out-of-band API calls and creating configuration drift between Terraform state and actual cluster configuration.

Describe the solution you'd like

Add a data_stream_options block inside the template block of elasticstack_elasticsearch_index_template. This should support at minimum the failure_store.enabled boolean.

Desired HCL syntax:

resource "elasticstack_elasticsearch_index_template" "example" {
  name           = "my-index-template"
  index_patterns = ["my-datastream-*"]

  template {
    data_stream_options {
      failure_store {
        enabled = true
      }
    }
  }

  data_stream {}
}

The corresponding Elasticsearch API:

PUT _index_template/my-index-template
{
  "index_patterns": ["my-datastream-*"],
  "data_stream": {},
  "template": {
    "data_stream_options": {
      "failure_store": {
        "enabled": true
      }
    }
  }
}

Describe alternatives you've considered

Using terraform_data with local-exec to GET the index template from Elasticsearch, patch in data_stream_options via jq, and PUT it back. This works but breaks infrastructure-as-code principles, requires curl/jq as dependencies, and creates drift between Terraform state and actual cluster configuration.

Additional context

• Elasticsearch documentation: https://www.elastic.co/docs/manage-data/data-store/data-streams/failure-store
• The data_stream_options field is part of the index template API starting in Elasticsearch 9.x
• Provider version tested: 0.14.3