Export `useSortBy` composable from helpers

### Describe the feature

`useSortBy` composable is not exported from 'pinia-orm/helpers'

### Additional information

- [X] Would you be willing to help implement this feature?

### Final checks

- [X] Check existing [discussions](https://github.com/CodeDredd/pinia-orm/discussions) and [issues](https://github.com/CodeDredd/pinia-orm/issues).