Adding custom_fields syncing

[Ianleeclark]

Motivation

We, as well as others, utilize braintree custom fields on our transactions [1] and we would like to be able to sync these to our database.

Design Considerations

The custom fields return as a string, so they can easily be stored into a custom_fields TEXT column. The hope is that this would be a simple PR just editing the schema, but I would first like to see if this would be a change which y'all are willing to accept and if there are any potential issues which you may see.

Either I or someone else at Packlane would be more than willing to make this PR and see it through the entire process.

[1] https://developers.braintreepayments.com/reference/request/transaction/sale/python#custom-fields

[KAllan357]

@GrappigPanda we'd definitely accept this PR. I think it would be as simple as adding an element to the transactions schema that would map custom fields to an empty schema: "custom_fields": {}

Would you need to do anything else to the Braintree API to retrieve these fields? For example, like adding a query-param that fetches them.

[Ianleeclark]

@KAllan357 Good to hear! The custom_fields field should return as a part of any transaction response https://developers.braintreepayments.com/reference/response/transaction/python

I'll try and get a PR submitted to you sometime tomorrow, barring any unforeseen circumstances.

Thanks again