Merge branch '211818-enable-streaming-serializer-ff' into 'master'

Enable streaming serializer for everybody by default

See merge request gitlab-org/gitlab!27813

app/services/projects/import_export/export_service.rb

@@ -58,7 +58,7 @@ module Projects
       end
 
       def tree_saver_class
-        if ::Feature.enabled?(:streaming_serializer, project)
+        if ::Feature.enabled?(:streaming_serializer, project, default_enabled: true)
           Gitlab::ImportExport::Project::TreeSaver
         else
           # Once we remove :streaming_serializer feature flag, Project::LegacyTreeSaver should be removed as well

changelogs/unreleased/211818-enable-streaming-serializer-ff.yml

+---
+title: Enable streaming serializer feature flag by default.
+merge_request: 27813
+author:
+type: performance