Added customer_notifications_preference and expiry_date on invoice.py

[Maulyanda]

Error:

1. _request() got an unexpected keyword argument 'expiry_date'
2. _request() got an unexpected keyword argument 'customer_notifications_preference'

Fixing:

1. added customer_notification_preference=None on invoice.py
2. added expiry_date=None on invoice.py

[msmur]

Hi @Maulyanda thanks for contributing, here's a list of changes I'll need you to make before I can approve this PR!

1. There is no 'expiry_date` argument in the create invoice request, you can check our api reference here: https://developers.xendit.co/api-reference/#create-invoice
2. Please comment the code appropriately, since you are adding a new argument you should update the function spec.

Lmk if you have any questions or if anything is unclear!

[Maulyanda]

HI @MESMUR, I've read the api reference documentation from xendit, it doesn't have an "expiry_date" in the documentation. But in the xendit application, the expiry date can be changed according to the user's wishes in creating invoices.

Changing the expiration date, is very necessary in the payment process in our company. If not, I will change my code again and not add an expiry date.