Change button text from "Create/add new role" to "Create role"

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/147507



Merged-by: David Pisek <dpisek@gitlab.com>
Approved-by: Vamsi Vempati <vvempati@gitlab.com>
Approved-by: Ilonah Pelaez <ipelaez@gitlab.com>
Approved-by: David Pisek <dpisek@gitlab.com>
Reviewed-by: Vamsi Vempati <vvempati@gitlab.com>
Reviewed-by: Ilonah Pelaez <ipelaez@gitlab.com>
Co-authored-by: Daniel Tian <dtian@gitlab.com>