Always create a new experiment for a model

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/144294



Merged-by: Dmitry Gruzd <dgruzd@gitlab.com>
Approved-by: Gregorius Marco <gmarco@gitlab.com>
Approved-by: Dmitry Gruzd <dgruzd@gitlab.com>
Reviewed-by: Darby Frey <dfrey@gitlab.com>
Reviewed-by: Gregorius Marco <gmarco@gitlab.com>
Co-authored-by: Darby Frey <dfrey@gitlab.com>
Co-authored-by: Gregorius Marco <gmarco@gitlab.com>
Co-authored-by: Eduardo Bonet <ebonet@gitlab.com>