[DOCS] Added job ID requirements (elastic/x-pack-elasticsearch#3727)

Original commit: elastic/x-pack-elasticsearch@71f0073708

docs/en/ml/troubleshooting.asciidoc

@@ -61,3 +61,26 @@ By default, {ml} results are stored in the `.ml-anomalies-shared` index in {es}.
 To resolve this issue, click *Advanced > Use dedicated index* when you create
 the job in {kib}. If you are using the create job API, specify an index name in
 the `results_index_name` property.
+
+[[ml-jobnames]]
+=== {kib} cannot display jobs with invalid characters in their name
+
+This problem occurs when you create a job by using the
+{ref}/ml-put-job.html[Create Jobs API] then try to view that job in {kib}. In
+particular, the problem occurs when you use a period(.) in the job identifier.
+
+*Symptoms:*
+
+* When you try to open a job (named, for example, `job.test` in the
+**Anomaly Explorer** or the **Single Metric Viewer**, the job name is split and
+the text after the period is assumed to be the job name. If a job does not exist
+with that abbreviated name, an error occurs. For example:
+`Warning Requested job test does not exist`. If a job exists with that
+abbreviated name, it is displayed.
+
+*Resolution:*
+
+Create jobs in {kib} or ensure that you create jobs with valid identifiers when
+you use the {ml} APIs. For more information about valid identifiers, see
+{ref}/ml-put-job.html[Create Jobs API] or
+{ref}/ml-job-resource.html[Job Resources].

docs/en/rest-api/ml/jobresource.asciidoc

@@ -49,7 +49,9 @@ so do not set the `background_persist_interval` value too low.
   many. For example, `["group1", "group2"]`.
 
 `job_id`::
-  (string) The unique identifier for the job.
+  (string) The unique identifier for the job. This identifier can contain
+  lowercase alphanumeric characters (a-z and 0-9), hyphens, and underscores. It
+  must start and end with alphanumeric characters.
 
 `job_type`::
   (string) Reserved for future use, currently set to `anomaly_detector`.

docs/en/rest-api/ml/put-job.asciidoc

@@ -16,7 +16,9 @@ This API enables you to instantiate a job.
 ==== Path Parameters
 
 `job_id` (required)::
-  (string) Identifier for the job
+  (string) Identifier for the job. This identifier can contain lowercase
+  alphanumeric characters (a-z and 0-9), hyphens, and underscores. It must
+  start and end with alphanumeric characters.
 
 
 ==== Request Body