Doc: Add info about push hooks limit

doc/api/settings.md

@@ -289,6 +289,7 @@ are listed in the descriptions of the relevant settings.
 | `prometheus_metrics_enabled`             | boolean          | no                                   | Enable Prometheus metrics. |
 | `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. |
 | `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/project/integrations/project_services.md

@@ -56,6 +56,16 @@ Click on the service links to see further configuration instructions and details
 | [Redmine](redmine.md) | Redmine issue tracker |
 | [YouTrack](youtrack.md) | YouTrack issue tracker |
 
+## Push hooks limit
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/issues/31009) in GitLab 12.4.
+
+If a single push includes changes to more than three branches or tags, services
+supported by `push_hooks` and `tag_push_hooks` events won't be executed.
+
+The number of branches or tags supported can be changed via
+[`push_event_hooks_limit` application setting](../../../api/settings.md#list-of-settings-that-can-be-accessed-via-api-calls).
+
 ## Services templates
 
 Services templates is a way to set some predefined values in the Service of

doc/user/project/integrations/webhooks.md

@@ -107,6 +107,9 @@ detailed commit data is expensive. Note that despite only 20 commits being
 present in the `commits` attribute, the `total_commits_count` attribute will
 contain the actual total.
 
+Also, if a single push includes changes for more than three (by default, depending on
+[`push_event_hooks_limit` setting](../../../api/settings.md#list-of-settings-that-can-be-accessed-via-api-calls)) branches, this hook won't be executed.
+
 **Request header**:
 
 ```
@@ -190,6 +193,10 @@ X-Gitlab-Event: Push Hook
 
 Triggered when you create (or delete) tags to the repository.
 
+NOTE: **Note:**
+If a single push includes changes for more than three (by default, depending on
+[`push_event_hooks_limit` setting](../../../api/settings.md#list-of-settings-that-can-be-accessed-via-api-calls)) tags, this hook won't be executed.
+
 **Request header**:
 
 ```