fix: conditionally set service domain outputs when disabled (#216)

Previously, service domain output locals were always set, even when the
module was disabled. This caused issues with downstream references. Now,
these locals are set to null when the module is not enabled, preventing
unintended values and improving conditional logic handling.

Author: RoseSecurity

main.tf

@@ -4,11 +4,11 @@ locals {
 
   service_linked_role_name = local.elasticsearch_enabled ? "AWSServiceRoleForAmazonElasticsearchService" : "AWSServiceRoleForAmazonOpenSearchService"
 
-  aws_service_domain_arn             = coalesce(join("", aws_elasticsearch_domain.default[*].arn), join("", aws_opensearch_domain.default[*].arn))
-  aws_service_domain_endpoint        = coalesce(join("", aws_elasticsearch_domain.default[*].endpoint), join("", aws_opensearch_domain.default[*].endpoint))
-  aws_service_domain_id              = coalesce(join("", aws_elasticsearch_domain.default[*].domain_id), join("", aws_opensearch_domain.default[*].domain_id))
-  aws_service_domain_name            = coalesce(join("", aws_elasticsearch_domain.default[*].domain_name), join("", aws_opensearch_domain.default[*].domain_name))
-  aws_service_domain_kibana_endpoint = coalesce(join("", aws_elasticsearch_domain.default[*].kibana_endpoint), join("", aws_opensearch_domain.default[*].dashboard_endpoint))
+  aws_service_domain_arn             = module.this.enabled ? coalesce(join("", aws_elasticsearch_domain.default[*].arn), join("", aws_opensearch_domain.default[*].arn)) : null
+  aws_service_domain_endpoint        = module.this.enabled ? coalesce(join("", aws_elasticsearch_domain.default[*].endpoint), join("", aws_opensearch_domain.default[*].endpoint)) : null
+  aws_service_domain_id              = module.this.enabled ? coalesce(join("", aws_elasticsearch_domain.default[*].domain_id), join("", aws_opensearch_domain.default[*].domain_id)) : null
+  aws_service_domain_name            = module.this.enabled ? coalesce(join("", aws_elasticsearch_domain.default[*].domain_name), join("", aws_opensearch_domain.default[*].domain_name)) : null
+  aws_service_domain_kibana_endpoint = module.this.enabled ? coalesce(join("", aws_elasticsearch_domain.default[*].kibana_endpoint), join("", aws_opensearch_domain.default[*].dashboard_endpoint)) : null
 }
 
 module "user_label" {