Creates a Customer Attribute. Multiple customer attributes can be created in one call.
Once the data type is set, it can not be changed. The attribute will need to be deleted then created again with the new data type. This will also delete it from the customer.
Customer attributes are created separately from the customer. After the name and type are created, then the attributes can be added to the customer.
A store cannot have more than 50 customer attributes.
Attribute type should match one of: string, number, date.