Staged Rollout Deployment for Amplify Hosted site

### Before opening, please confirm:

- [X] I have checked to see if my question is addressed in the [FAQ](https://github.com/aws-amplify/amplify-hosting/blob/master/FAQ.md).
- [X] I have [searched for duplicate or closed issues](https://github.com/aws-amplify/amplify-hosting/issues?q=is%3Aissue+).
- [X] I have removed any sensitive information from my code snippets and submission.

### Amplify Hosting feature

Deployments

### Is your feature request related to a problem? Please describe:

When a new feature need to be deployed, a way to deploy it as staged rollout i.e, first migrating 10% of traffic and increasing slowly

Amplify currently support atomic deploys and instant cache invalidation but not staged rollout deployment

### Describe how you'd like this feature to work

To have staged rollout deployment with Amplify hosted site