Add index.unassigned.node_left.delayed_timeout

[yoavshemesh-riskified]

Is your feature request related to a problem? Please describe.
Please add the index settings
"index.unassigned.node_left.delayed_timeout"
as described here https://www.elastic.co/guide/en/elasticsearch/reference/current/delayed-allocation.html

Describe the resource you would like to have implemented.
The Terraform resource is "elasticstack_elasticsearch_index"

Describe the solution you'd like
Please add it as an optional parameter as described here https://registry.terraform.io/providers/elastic/elasticstack/latest/docs/resources/elasticsearch_index#optional

Describe alternatives you've considered
For now, we are using a deprecated option of settings
settings {
setting {
name = "index.unassigned.node_left.delayed_timeout"
value = "5m"
}
}
Even-though it is not mentioned at the module it self
https://github.com/elastic/terraform-provider-elasticstack/blob/main/internal/elasticsearch/index/index.go

Our concern is that this option will be removed in the next versions.

Thank you for a great TF provider.