data-external feature of Terraform has helped me

cat owner.sh

jq -n --arg username $(git config user.name) '{"username": $username}'

The config part which must be added on instance_create.tf files;

data "external" "owner_tag_generator" {
  program = ["bash", "/full/path/of/owner.sh"]
}

output "owner" {
  value = "${data.external.owner_tag_generator.result}"
}

tags {
...
CreatorName = "${data.external.owner_tag_generator.result.username}"
...
}