Update Metrics Dictionary guide

doc/development/usage_ping/metrics_dictionary.md

@@ -27,6 +27,7 @@ Each metric is defined in a separate YAML file consisting of a number of fields:
 | Field               | Required | Additional information                                         |
 |---------------------|----------|----------------------------------------------------------------|
 | `key_path`          | yes      | JSON key path for the metric, location in Usage Ping payload.  |
+| `name`              | no       | Metric name suggestion. Can replace the last part of `key_path`. |
 | `description`       | yes      |                                                                |
 | `product_section`   | yes      | The [section](https://gitlab.com/gitlab-com/www-gitlab-com/-/blob/master/data/sections.yml). |
 | `product_stage`     | no       | The [stage](https://gitlab.com/gitlab-com/www-gitlab-com/blob/master/data/stages.yml) for the metric. |
@@ -54,6 +55,80 @@ 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 name
+
+To improve metric discoverability by a wider audience, each metric with
+instrumentation added at an appointed `key_path` receives a `name` attribute
+filled with the name suggestion, corresponding to the metric `data_source` and instrumentation.
+Metric name suggestions can contain two types of elements:
+
+1. **User input prompts**: Enclosed by `<>`, these pieces should be replaced or
+   removed when you create a metrics YAML file.
+1. **Fixed suggestion**: Plaintext parts generated according to well-defined algorithms.
+   They are based on underlying instrumentation, and should not be changed.
+
+For a metric name to be valid, it must not include any prompt, and no fixed suggestions
+should be changed.
+
+### Metric name suggestion examples
+
+#### Metric with `data_source: database`
+
+For a metric instrumented with SQL:
+
+```sql
+SELECT COUNT(DISTINCT user_id) FROM clusters WHERE clusters.management_project_id IS NOT NULL
+```
+
+- **Suggested name**: `count_distinct_user_id_from_<adjective describing: '(clusters.management_project_id IS NOT NULL)'>_clusters`
+- **Prompt**: `<adjective describing: '(clusters.management_project_id IS NOT NULL)'>`
+  should be replaced with an adjective that best represents filter conditions, such as `project_management`
+- **Final metric name**: For example, `count_distinct_user_id_from_project_management_clusters`
+
+For metric instrumented with SQL:
+
+```sql
+SELECT COUNT(DISTINCT clusters.user_id)
+FROM clusters_applications_helm
+INNER JOIN clusters ON clusters.id = clusters_applications_helm.cluster_id
+WHERE clusters_applications_helm.status IN (3, 5)
+```
+
+- **Suggested name**: `count_distinct_user_id_from_<adjective describing: '(clusters_applications_helm.status IN (3, 5))'>_clusters_<with>_<adjective describing: '(clusters_applications_helm.status IN (3, 5))'>_clusters_applications_helm`
+- **Prompt**: `<adjective describing: '(clusters_applications_helm.status IN (3, 5))'>`
+  should be replaced with an adjective that best represents filter conditions
+- **Final metric name**: `count_distinct_user_id_from_clusters_with_available_clusters_applications_helm`
+
+In the previous example, the prompt is irrelevant, and user can remove it. The second
+occurrence corresponds with the `available` scope defined in `Clusters::Concerns::ApplicationStatus`.
+It can be used as the right adjective to replace prompt.
+
+The `<with>` represents a suggested conjunction for the suggested name of the joined relation.
+The person documenting the metric can use it by either:
+
+- Removing the surrounding `<>`.
+- Using a different conjunction, such as `having` or `including`.
+
+#### Metric with `data_source: redis` or `redis_hll`
+
+For metrics instrumented with a Redis-based counter, the suggested name includes
+only the single prompt to be replaced by the person working with metrics YAML.
+
+- **Prompt**: `<please fill metric name, suggested format is: {subject}_{verb}{ing|ed}_{object} eg: users_creating_epics or merge_requests_viewed_in_single_file_mode>`
+- **Final metric name**: We suggest the metric name should follow the format of
+  `{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`
+
+For metrics instrumented with Prometheus or Ruby, 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,
+  no naming convention exists. Each person instrumenting a metric should use their
+  best judgment to come up with a descriptive name.
+
 ### Example YAML metric definition
 
 The linked [`uuid`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/config/metrics/license/uuid.yml)