Add new cop Gitlab/Rails/SafeFormat

See merge request !121313



Merged-by: Peter Leitzen <pleitzen@gitlab.com>
Approved-by: Diogo Frazão <dfrazao@gitlab.com>
Approved-by: Costel Maxim <cmaxim@gitlab.com>
Approved-by: Smriti Garg <sgarg@gitlab.com>
Approved-by: Rémy Coutable <remy@rymai.me>
Reviewed-by: Rémy Coutable <remy@rymai.me>