Reading through these docs it calls out that the Org Master account needs to define the delegate administrator account, but looking at these resources in the terraform provider, I don't see how you would declare your delegate administrator account? Using terraform, how would you declare a delegate administrator account with the given arguments available here?
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/securitylake_data_lake
There is a resource for what you need:
resource "aws_organizations_delegated_administrator" "security_lake" {
account_id = <some AWS account ID>
service_principal = "securitylake.amazonaws.com"
}
There is also this document from AWS with more details.