Merge branch 'cluster-annotations-create-api-docs' into 'master'

Add cluster annotations api documentation

See merge request gitlab-org/gitlab!29508

doc/api/api_resources.md

@@ -132,7 +132,7 @@ The following API resources are available outside of project and group contexts
 | [License](license.md) **(CORE ONLY)**              | `/license`                                                              |
 | [Markdown](markdown.md)                            | `/markdown`                                                             |
 | [Merge requests](merge_requests.md)                | `/merge_requests` (also available for groups and projects)              |
-| [Metrics dashboard annotations](metrics_dashboard_annotations.md)    | `/environments/:id/metrics_dashboard/annotations`     |
+| [Metrics dashboard annotations](metrics_dashboard_annotations.md) | `/environments/:id/metrics_dashboard/annotations`, `/clusters/:id/metrics_dashboard/annotations` |
 | [Namespaces](namespaces.md)                        | `/namespaces`                                                           |
 | [Notification settings](notification_settings.md)  | `/notification_settings` (also available for groups and projects)       |
 | [Pages domains](pages_domains.md)                  | `/pages/domains` (also available for projects)                          |

doc/api/metrics_dashboard_annotations.md

@@ -18,6 +18,7 @@ Feature.enable(:metrics_dashboard_annotations)
 
 ```plaintext
 POST /environments/:id/metrics_dashboard/annotations/
+POST /clusters/:id/metrics_dashboard/annotations/
 ```
 
 Parameters: