Doc: Update doc about the new limit

Add information in admin area and API sections.

doc/api/settings.md

@@ -290,6 +290,7 @@ are listed in the descriptions of the relevant settings.
 | `protected_ci_variables`                 | boolean          | no                                   | Environment variables are protected by default. |
 | `pseudonymizer_enabled`                  | boolean          | no                                   | **(PREMIUM)** When enabled, GitLab will run a background job that will produce pseudonymized CSVs of the GitLab database that will be uploaded to your configured object storage directory.
 | `push_event_hooks_limit`                 | integer          | no                                   | Number of changes (branches or tags) in a single push to determine whether webhooks and services will be fired or not. Webhooks and services won't be submitted if it surpasses that value. |
+| `push_event_activities_limit`            | integer          | no                                   | Number of changes (branches or tags) in a single push to determine whether individual push events or bulk push events will be created. [Bulk push events will be created](../user/admin_area/settings/push_event_activities_limit.md) if it surpasses that value. |
 | `recaptcha_enabled`                      | boolean          | no                                   | (**If enabled, requires:** `recaptcha_private_key` and `recaptcha_site_key`) Enable reCAPTCHA. |
 | `recaptcha_private_key`                  | string           | required by: `recaptcha_enabled`     | Private key for reCAPTCHA. |
 | `recaptcha_site_key`                     | string           | required by: `recaptcha_enabled`     | Site key for reCAPTCHA. |

doc/user/admin_area/settings/index.md

@@ -22,6 +22,7 @@ include:
 - [Custom templates repository](instance_template_repository.md) **(PREMIUM)**
 - [Protected paths](protected_paths.md) **(CORE ONLY)**
 - [Help messages for the `/help` page and the login page](help_page.md)
+- [Push event activities limit and bulk push events](push_event_activities_limit.md)
 
 NOTE: **Note:**
 You can change the [first day of the week](../../profile/preferences.md) for the entire GitLab instance

doc/user/admin_area/settings/push_event_activities_limit.md

+---
+type: reference
+---
+
+# Push event activities limit and bulk push events
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/issues/31007) in GitLab 12.4.
+
+This allows you to set the number of changes (branches or tags) in a single push
+to determine whether individual push events or bulk push event will be created.
+Bulk push events will be created if it surpasses that value.
+
+For example, if 4 branches are pushed and the limit is currently set to 3,
+you'll see the following in the activity feed:
+
+![Bulk push event](img/bulk_push_event_v12_4.png)
+
+With this feature, when a single push includes a lot of changes (e.g. 1,000
+branches), only 1 bulk push event will be created instead of creating 1,000 push
+events. This helps in maintaining good system performance and preventing spam on
+the activity feed.
+
+This setting can be modified in **Admin Area > Settings > Network > Performance Optimization**.
+This can also be configured via the [Application settings API](../../../api/settings.md#list-of-settings-that-can-be-accessed-via-api-calls)
+as `push_event_activities_limit`. The default value is 3, but it can be greater
+than or equal 0.
+
+![Push event activities limit](img/push_event_activities_limit_v12_4.png)