Enable ci_pipeline_editor_page by default

This change enables feature flag ci_pipeline_editor_page by default and
updates documentation to indicate this.

changelogs/unreleased/270059-feature-flag-rollout-of-ci_pipeline_editor_page.yml

+---
+title: Enables the CI Pipeline Editor feature as a way to edit the GitLab CI/CD configuration
+merge_request: 51484
+author:
+type: added

config/feature_flags/development/ci_pipeline_editor_page.yml

@@ -5,4 +5,4 @@ rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/270059
 milestone: '13.6'
 type: development
 group: group::pipeline authoring
-default_enabled: false
+default_enabled: true

doc/ci/pipeline_editor/index.md

@@ -8,8 +8,8 @@ type: reference
 # Pipeline Editor **(CORE)**
 
 > - [Introduced](https://gitlab.com/groups/gitlab-org/-/epics/4540) in GitLab 13.8.
-> - It's [deployed behind a feature flag](../../user/feature_flags.md), disabled by default.
-> - It's disabled on GitLab.com.
+> - It's [deployed behind a feature flag](../../user/feature_flags.md), enabled by default.
+> - It's enabled on GitLab.com.
 > - It's not recommended for production use.
 > - To use it in GitLab self-managed instances, ask a GitLab administrator to [enable it](#enable-or-disable-pipeline-editor). **(CORE ONLY)**
 
@@ -115,18 +115,18 @@ checkbox appears. Select it to start a new merge request after you commit the ch
 ## Enable or disable pipeline editor **(CORE ONLY)**
 
 The pipeline editor is under development and not ready for production use. It is
-deployed behind a feature flag that is **disabled by default**.
+deployed behind a feature flag that is **enabled by default**.
 [GitLab administrators with access to the GitLab Rails console](../../administration/feature_flags.md)
-can enable it.
+can disable it.
 
-To enable it:
+To disable it:
 
 ```ruby
-Feature.enable(:ci_pipeline_editor_page)
+Feature.disable(:ci_pipeline_editor_page)
 ```
 
-To disable it:
+To enable it:
 
 ```ruby
-Feature.disable(:ci_pipeline_editor_page)
+Feature.enable(:ci_pipeline_editor_page)
 ```

lib/gitlab/ci/features.rb

@@ -60,7 +60,7 @@ module Gitlab
       end
 
       def self.ci_pipeline_editor_page_enabled?(project)
-        ::Feature.enabled?(:ci_pipeline_editor_page, project, default_enabled: false)
+        ::Feature.enabled?(:ci_pipeline_editor_page, project, default_enabled: :yaml)
       end
 
       def self.allow_failure_with_exit_codes_enabled?