Add tier badges to Sidekiq API topics

doc/api/admin_sidekiq_queues.md

-# Admin Sidekiq queues API
+# Sidekiq queues administration API **(CORE ONLY)**
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/25998) in GitLab 12.9
 
@@ -15,7 +15,7 @@ The response has three fields:
    delete further jobs (including those added after the first request
    was issued).
 
-This API endpoint is only available to admin users.
+This API endpoint is only available to administrators.
 
 ```plaintext
 DELETE /admin/sidekiq/queues/:queue_name

doc/api/api_resources.md

@@ -116,7 +116,7 @@ The following API resources are available outside of project and group contexts
 | Resource                                           | Available endpoints                                                     |
 |:---------------------------------------------------|:------------------------------------------------------------------------|
 | [Instance-level CI/CD variables](instance_level_ci_variables.md) | `/admin/ci/variables`                                     |
-| [Admin Sidekiq queues](admin_sidekiq_queues.md)    | `/admin/sidekiq/queues/:queue_name`                                     |
+| [Sidekiq queues administration](admin_sidekiq_queues.md) **(CORE ONLY)** | `/admin/sidekiq/queues/:queue_name`               |
 | [Appearance](appearance.md) **(CORE ONLY)**        | `/application/appearance`                                               |
 | [Applications](applications.md)                    | `/applications`                                                         |
 | [Audit Events](audit_events.md) **(PREMIUM ONLY)** | `/audit_events`                                                         |
@@ -148,7 +148,7 @@ The following API resources are available outside of project and group contexts
 | [Search](search.md)                                | `/search` (also available for groups and projects)                      |
 | [Settings](settings.md) **(CORE ONLY)**            | `/application/settings`                                                 |
 | [Statistics](statistics.md)                        | `/application/statistics`                                               |
-| [Sidekiq metrics](sidekiq_metrics.md)              | `/sidekiq`                                                              |
+| [Sidekiq metrics](sidekiq_metrics.md) **(CORE ONLY)** | `/sidekiq`                                                           |
 | [Suggestions](suggestions.md)                      | `/suggestions`                                                          |
 | [System hooks](system_hooks.md)                    | `/hooks`                                                                |
 | [Todos](todos.md)                                  | `/todos`                                                                |

doc/api/sidekiq_metrics.md

-# Sidekiq Metrics API
+# Sidekiq Metrics API **(CORE ONLY)**
 
 > Introduced in GitLab 8.9.