[Docs]: Add explanation for `/url` property in Aria Snapshot

### Page(s)

https://playwright.dev/docs/aria-snapshots#snapshot-matching

### Description

In [v1.52](https://playwright.dev/docs/release-notes#version-152) this new `/url` property was added. The release notes do show a quick example of this, but this should also be added to the Aria Snapshots page.