Add Snaps lifecycle hooks feature page

Add a topic under **Snaps > Features** describing how to create lifecycle hooks using the `endowment:lifecycle-hooks` permission and `onInstall` and `onUpdate` entry points. Link to the [lifecycle hooks example package](https://github.com/MetaMask/snaps/tree/main/packages/examples/packages/lifecycle-hooks). The lifecycle hooks card on the Snaps intro page should link to this feature page.