Workflows: Allow specifying the HTTP status code

Is your feature request related to a problem? Please describe. Currently workflows either return a HTTP 500 for any error or HTTP 200 for success. I'd like to be able to specify the status code to reflect more of what happened inside the workflow. For example:

• "Namespace provisioning" -> should return 201
• "Namespace deletion" -> should return 404 if path wasn't found

Describe the solution you'd like Within the output block we could add a new parameter status_code:

output {
  status_code = 201
  // or
  status_code = {
    eval_type = "int"
    eval_source = "cel"
    expression = "..."
  }

  data = { ... }
  headers = { ... }
}