Marks job_type in anomaly job config as a private parameter (#5287)

* Marks job_type in anomaly job config as private.

* Edits.

(cherry picked from commit 1978d33)

Author: szabosteve

specification/ml/_types/Job.ts

@@ -242,6 +242,8 @@ export class JobConfig {
   job_id?: Id
   /**
    * Reserved for future use, currently set to `anomaly_detector`.
+   * @availability stack visibility=private
+   * @availability serverless visibility=private
    */
   job_type?: string
   /**