clientv3/compare.go
func (cmp Cmp) WithPrefix() Cmp {
	cmp.RangeEnd = getPrefix(cmp.Key)
	return cmp
}
func (cmp Cmp) WithPrefix() Cmp {
	cmp.RangeEnd = getPrefix(cmp.Key)
	return cmp
}
// WithPrefix sets the comparison to scan all keys prefixed by the key.