Add transaction model to ProcessPaymentEvent

[lukeholder]

Adding the transaction model to the event will allow a developer to dynamically override the transaction’s paymentType and set it to either purchase or authorize. (The default will be set to the gateway’s payment type in config)

https://github.com/craftcms/commerce/blob/develop/src/services/Payments.php#L243

[rynpsc]

Has this feature made its way into Commerce yet? We could do with this for a project we are working on where some users payments will be just captured whist others will be authorised as well.