ListOptOutListRequest

E.164-validate contact_number / sender_whatsapp_number on input.

Shared by the create and update serializers so an invalid number is rejected
with a 400 on POST and PATCH/PUT -- otherwise the model's normalize_number()
silently digit-strips junk (e.g. "helw" -> "") on save instead of erroring.

{ "contact_number": "string", "sender_whatsapp_number": "string", "message_id": "string", "opted_out_global": true, "opted_out_promotions": true, "opted_out_news": true, "opted_out_events": true, "opted_out_surveys": true, "origin": "INBOUND_STOP", "created_by": "string", "reason": "string" }