Make fixed pipeline notification default enabled

This commit makes the fixed pipeline notification default enabled

changelogs/unreleased/make-fixed-notification-default-enabled.yml

+---
+title: Send fixed pipeline notification by default
+merge_request: 34589
+author:
+type: added

doc/user/profile/notifications.md

@@ -187,7 +187,7 @@ To minimize the number of notifications that do not require any action, from [Gi
 | Remove milestone merge request | Subscribers, participants mentioned, and Custom notification level with this event selected |
 | New comment            | The above, plus anyone mentioned by `@username` in the comment, with notification level "Mention" or higher |
 | Failed pipeline        | The author of the pipeline |
-| Fixed pipeline    | The author of the pipeline. Disabled by default. To activate it you must [enable the `ci_pipeline_fixed_notifications` feature flag](../../development/feature_flags/development.md#enabling-a-feature-flag-in-development). |
+| Fixed pipeline    | The author of the pipeline. Enabled by default. |
 | Successful pipeline    | The author of the pipeline, if they have the custom notification setting for successful pipelines set. If the pipeline failed previously, a `Fixed pipeline` message will be sent for the first successful pipeline after the failure, then a `Successful pipeline` message for any further successful pipelines. |
 | New epic **(ULTIMATE)** |        |
 | Close epic **(ULTIMATE)** |      |

lib/gitlab/ci/features.rb

@@ -23,7 +23,7 @@ module Gitlab
       end
 
       def self.pipeline_fixed_notifications?
-        ::Feature.enabled?(:ci_pipeline_fixed_notifications)
+        ::Feature.enabled?(:ci_pipeline_fixed_notifications, default_enabled: true)
       end
 
       def self.instance_variables_ui_enabled?