[DOC] - Fax error codes not provided in Docs

[ChrisKlacsanzky-SignalWire]

Describe the requested update
A customer reached out saying they wished we provided the error code for faxes in our docs, right now we just provide the error message type: https://developer.signalwire.com/fax/getting-started/common-fax-errors/

Reason for the request
Other services provide error codes like messaging.

Sections to be updated
all sections can have error code along with the error messaging.