Merge branch 'jnutt/enable-csv-by-default' into 'master'

Enable importer_user_mapping_reassignment_csv flag by default

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/184169



Merged-by: Rodrigo Tomonari <rtomonari@gitlab.com>
Approved-by: Rodrigo Tomonari <rtomonari@gitlab.com>
Reviewed-by: Ashraf Khamis <akhamis@gitlab.com>
Co-authored-by: James Nutt <jnutt@gitlab.com>