Changes to Upload files to existing collection

added the new PCS_ORDERS enum value to the documents/items/document_type response property for the response status 201

added the new F1099_B enum value to the documents/items/document_subtype response property for the response status 201

added the new F1099_K enum value to the documents/items/document_subtype response property for the response status 201

the documents/items/user_id request property's maxLength was decreased to 32

the response property documents/items/end_page became nullable for the status 201

the response property documents/items/start_page became nullable for the status 201