I have the following terraform script which creates Elastic Beanstalk with rds:

resource "aws_elastic_beanstalk_application" "elb_app" {
  name = "my-app"

}


resource "aws_elastic_beanstalk_environment" "elb_env" {
  name                = "my-env"
  application         = aws_elastic_beanstalk_application.elb_app.name
  solution_stack_name = data.aws_elastic_beanstalk_solution_stack.net_latest.name
  
  setting {
    namespace = "aws:elasticbeanstalk:application:environment"
    name      = "RDS_HOSTNAME"
    value     = #  How can I set here the RDS endpoint ???
  }

  setting {
    namespace = "aws:rds:dbinstance"
    name      = "HasCoupledDatabase"
    value     = "true"
  }

  setting {
    namespace = "aws:rds:dbinstance"
    name      = "DBEngine"
    value     = var.db_engine
  }

  setting {
    namespace = "aws:rds:dbinstance"
    name      = "DBEngineVersion"
    value     = var.db_engine_version
  }

  setting {
    namespace = "aws:rds:dbinstance"
    name      = "DBInstanceClass"
    value     = var.db_instance_type
  }

  setting {
    namespace = "aws:rds:dbinstance"
    name      = "DBPassword"
    value     = var.db_password
  }

  setting {
    namespace = "aws:rds:dbinstance"
    name      = "DBUser"
    value     = var.db_user
  }
 }

The question is: how can I set the RDS_HOSTNAME ?

As far as I know, it is possible to get the endpoint from an RDS created as a separate resource, but I didn’t find any documentation how to get this from RDS created as part of an Elastic Beanstalk.
I spent many days and didn’t find any example however it should be a typical case for developers.