Enable syncing epic to work items by default

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/152627



Merged-by: Felipe Artur <fcardozo@gitlab.com>
Approved-by: Abhilash Kotte <akotte@gitlab.com>
Approved-by: Felipe Artur <fcardozo@gitlab.com>
Co-authored-by: Nicolas Dular <ndular@gitlab.com>