Changes to List subscribers

the query request parameter sort_field was restricted to a list of enum values

added the new enum value canceled_at to the query request parameter sort_field

added the new enum value cancelled_at to the query request parameter sort_field

added the new enum value created_at to the query request parameter sort_field

added the new enum value engagement__click_rate to the query request parameter sort_field

added the new enum value engagement__clicks to the query request parameter sort_field

added the new enum value engagement__open_rate to the query request parameter sort_field

added the new enum value engagement__opens to the query request parameter sort_field

added the new enum value engagement__sent to the query request parameter sort_field

added the new enum value id to the query request parameter sort_field

added the new enum value updated_at to the query request parameter sort_field