This pr introduces MPesa payment methods using Safaricom APIs for Kenya.

There are two types of payment methods :

- Mpesa Express: This is implemented with the M-Pesa Express API. It's the Merchant Initiated payment method. The merchant create a payment method M-Pesa Express with Safaricom payment provider. The merchant is allowed to ask for payment through the API with an USSD prompt on the customer phone number. Customer enters the PIN and the API call the callback of the POS to reconcile transaction with order. (https://daraja.safaricom.co.ke/dashboard/apis?api=MpesaExpressSimulate)

- Lipa Na Mpesa: This is implemented with the Customer To Business (C2B) API. This payment method is different from the first one. It is a Merchant-Initiated payment method. The POS registers callback URLs through the register URL. The POS listen on its callbacks. Customer sends a payment through his Safaricom or MPesa application with some informations of the business. When a transaction is catch in the callback, POS displays it. The cashier needs, manually, to reconcile it with the current order. To reconcile, cashier see a popup with every transaction done on this business account number. (https://daraja.safaricom.co.ke/dashboard/apis?api=CustomerToBusiness)

Dynamic QR Code API is also implemented to allow customers to scan the QR Code in the official Safaricom application and send the payment easily without errors of amount or till number. (https://daraja.safaricom.co.ke/dashboard/apis?api=DynamicQRCode)

Note : The problem with this payment method is that there is two steps. The first step is a "Verification" step, which is optional. Businesses needs to manually sends an email to Safaricom to allows them to add this step. This step is useful because it is used to accept or reject a transaction before charging the customer. But, in reality, not all of the businesses ask Safaricom to add this step. So, we don't configure it for the moment. The second step is the "Confirmation" step, before this step, the customer is already charged. The API sends transaction data to the POS, we display it in the POS to allow cashier to reconcile the current order with a transaction.

Requirements : If you want to test this API, https is needed and a valid kenyan (+254) phone number is also needed. But, you can simulate requests in the Daraja Portal. (https://daraja.safaricom.co.ke/dashboard/apis)

task: 5886047

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Forward-Port-Of: odoo/odoo#247615