Fix: Webhook updates are appending fields rather than updating in place

[ericdrosas87]

Currently when an asset in Canto is updated and the webhook is triggered the field updated is appended rather than updated in place. This may be isolated to the credit field, but may widespread across all fields. This fix ensures the webhook updates update an asset field in-place.

[khalwat]

Can you clarify this a bit for me? Perhaps with a before/after example in terms of what happens and what you're expecting to have happen?