Create a multi-step approval flow on a job (and optionally a specific offer), seeded with the supplied approver groups. Each job allows at most one flow per approval_type: one open_job flow gating job opening, one offer_job flow gating offer creation, and one offer_candidate prototype on the job plus one offer_candidate flow per offer (set offer_id for the latter). The new flow is created in pending status with no emails sent; call POST /v3/approval_flows/{id}/request_approvals to actually start it. Each approver entry may identify a user by user_id, email, or employee_id, but the same user cannot appear in more than one group of the same flow.