Merge branch '326717-add-docs-in-metrics-dictionary-for-object-value-type' into 'master'

Add docs in metrics dictionary for object value type

See merge request gitlab-org/gitlab!62462

doc/development/usage_ping/metrics_dictionary.md

@@ -57,6 +57,18 @@ Metric definitions can have one of the following statuses:
 - `deprecated`: Metric is deprecated and possibly planned to be removed.
 - `removed`: Metric was removed, but it may appear in Usage Ping payloads sent from instances running on older versions of GitLab.
 
+### Metric value_type
+
+Metric definitions can have one of the following values for `value_type`:
+
+- `boolean`
+- `number`
+- `string`
+- `object`: A metric with `value_type: object` must have `value_json_schema` with a link to the JSON schema for the object.
+In general, we avoid complex objects and prefer one of the `boolean`, `number`, or `string` value types.
+An example of a metric that uses `value_type: object` is `topology` (`/config/metrics/settings/20210323120839_topology.yml`),
+which has a related schema in `/config/metrics/objects_schemas/topology_schema.json`.
+
 ### Metric name
 
 To improve metric discoverability by a wider audience, each metric with