Add system as data_source type in metric definitions

config/metrics/schema.json

@@ -49,7 +49,7 @@
     },
     "data_source": {
       "type": "string",
-      "enum": ["database", "redis", "redis_hll", "prometheus", "ruby"]
+      "enum": ["database", "redis", "redis_hll", "prometheus", "ruby", "system"]
     },
     "distribution": {
       "type": "array",

doc/development/usage_ping/metrics_dictionary.md

@@ -36,7 +36,7 @@ Each metric is defined in a separate YAML file consisting of a number of fields:
 | `value_type`        | yes      | `string`; one of [`string`, `number`, `boolean`, `object`](https://json-schema.org/understanding-json-schema/reference/type.html).                                                     |
 | `status`            | yes      | `string`; [status](#metric-statuses) of the metric, may be set to `data_available`, `implemented`, `not_used`, `deprecated`, `removed`. |
 | `time_frame`        | yes      | `string`; may be set to a value like `7d`, `28d`, `all`, `none`. |
-| `data_source`       | yes      | `string`; may be set to a value like `database`, `redis`, `redis_hll`, `prometheus`, `ruby`. |
+| `data_source`       | yes      | `string`; may be set to a value like `database`, `redis`, `redis_hll`, `prometheus`, `ruby`, `system`. |
 | `distribution`      | yes      | `array`; may be set to one of `ce, ee` or `ee`. The [distribution](https://about.gitlab.com/handbook/marketing/strategic-marketing/tiers/#definitions) where the tracked feature is available.  |
 | `tier`              | yes      | `array`; may be set to one of `free, premium, ultimate`, `premium, ultimate` or `ultimate`. The [tier]( https://about.gitlab.com/handbook/marketing/strategic-marketing/tiers/) where the tracked feature is available. |
 | `milestone`         | no       | The milestone when the metric is introduced. |
@@ -119,10 +119,10 @@ only the single prompt to be replaced by the person working with metrics YAML.
   `{subject}_{verb}{ing|ed}_{object}`, such as `user_creating_epics`, `users_triggering_security_scans`,
   or `merge_requests_viewed_in_single_file_mode`
 
-#### Metric with `data_source: prometheus` or `ruby`
+#### Metric with `data_source: prometheus`, `ruby` or `system`
 
-For metrics instrumented with Prometheus or Ruby, the suggested name includes only
-the single prompt by person working with metrics YAML.
+For metrics instrumented with Prometheus or Ruby, or coming from the operating system,
+the suggested name includes only the single prompt by person working with metrics YAML.
 
 - **Prompt**: `<please fill metric name>`
 - **Final metric name**: Due to the variety of cases that can apply to this kind of metric,