get https://example.com/consumer/v1/customers/customfields
This end point returns your Customer custom field definitions.
Customer custom fields are different than Appointment custom fields. Appointment custom fields are
stored with each appointment. They are used when the information collected during the booking is specific
to a particular visit, where as Customer custom fields are stored with the customer profile.
Use the key field, and type to determine how to update field values
in POST /consumer/v1/customers and PUT /consumer/v1/customers/{id}