Enables one_dimensional_matrix ff by default

config/feature_flags/development/one_dimensional_matrix.yml

@@ -4,4 +4,4 @@ introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/42170
 rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/256062
 type: development
 group: group::pipeline authoring
-default_enabled: false
+default_enabled: true

doc/ci/yaml/README.md

@@ -3587,8 +3587,7 @@ There can be from 2 to 50 jobs.
 [In GitLab 13.5](https://gitlab.com/gitlab-org/gitlab/-/issues/26362) and later,
 you can have one-dimensional matrices with a single job.
 The ability to have one-dimensional matrices is [deployed behind a feature flag](../../user/feature_flags.md),
-disabled by default. It's disabled on GitLab.com. To use it in a GitLab self-managed
-instance, ask a GitLab administrator to [enable the `one_dimensional_matrix:` feature flag](../../administration/feature_flags.md). **(CORE ONLY)**
+enabled by default. It's enabled on GitLab.com.  **(CORE ONLY)**
 
 Every job gets the same `CI_NODE_TOTAL` [environment variable](../variables/README.md#predefined-environment-variables) value, and a unique `CI_NODE_INDEX` value.
 

lib/gitlab/ci/features.rb

@@ -68,7 +68,7 @@ module Gitlab
       end
 
       def self.one_dimensional_matrix_enabled?
-        ::Feature.enabled?(:one_dimensional_matrix, default_enabled: false)
+        ::Feature.enabled?(:one_dimensional_matrix, default_enabled: true)
       end
 
       def self.manual_bridges_enabled?(project)