Switch load_balancing_atomic_replica feature flag on by default

This feature flag has been on in GitLab.com for over a week and has
likely prevented failed merges due to stale replicas. We switch this
feature flag on by default.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/291193

config/feature_flags/development/load_balancing_atomic_replica.yml

@@ -4,5 +4,5 @@ introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/49294
 rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/291193
 milestone: '13.11'
 type: development
-group:
-default_enabled: false
+group: group::database
+default_enabled: true

ee/changelogs/unreleased/sh-enable-load-balancing-atomic-replica-ff.yml

+---
+title: Switch load_balancing_atomic_replica feature flag on by default
+merge_request: 60574
+author:
+type: fixed

ee/lib/ee/gitlab/checks/matching_merge_request.rb

@@ -28,7 +28,7 @@ module EE
           # report no matching merge requests. To avoid this, we check
           # the write location to ensure the replica can make this query.
           track_session_metrics do
-            if ::Feature.enabled?(:load_balancing_atomic_replica, @project)
+            if ::Feature.enabled?(:load_balancing_atomic_replica, @project, default_enabled: :yaml)
               ::Gitlab::Database::LoadBalancing::Sticking.select_valid_host(:project, @project.id)
             else
               ::Gitlab::Database::LoadBalancing::Sticking.unstick_or_continue_sticking(:project, @project.id)