Smooth scroll an item into view

### Clear and concise description of the problem

- Currently the library has a scrollToItem method but the behavior is not smooth

### Suggested solution

- Implement a function to smooth scroll into view

### Alternative

_No response_

### Additional context

Something [like this](https://codepen.io/rleve/pen/jObeRN) but for the virtual scroller. Found nothing [here](https://github.com/Akryum/vue-virtual-scroller/issues?q=is%3Aissue+is%3Aopen+smooth)

### Validations

- [X] Read the [docs](https://github.com/Akryum/vue-virtual-scroller/blob/master/packages/vue-virtual-scroller/README.md).
- [X] Check that there isn't [already an issue](https://github.com/Akryum/vue-virtual-scroller/issues) that reports the same bug to avoid creating a duplicate.