[Docs]: add example of custom list with DataSources

[AlekseyManetov]

Description

Let's add one more example to the Usage in components datasource page. This example will describe how to implement your own list based on DataSources and VirtualList component. Draft version: https://codesandbox.io/s/uui-lazyds-virtuallist-custom-items-8l6vl3?file=/Example.tsx