Docs: Interactivity API - "@wordpress/interactivity-router" README needs to be updated to reflect is not experimental anymore

In the README of `@wordpress/interactivity-router` we can read things such as

> [Can I use it?](https://developer.wordpress.org/block-editor/reference-guides/packages/packages-interactivity-router/#can-i-use-it)
> You can test it, but it’s still very experimental.

This README needs to be reviewed and updated to its latest state