FR (Authenticator): preferPrivateSession option for React Native

### On which framework/platform would you like to see this feature implemented?

React Native

### Which UI component is this feature-request for?

Authenticator

### Please describe your feature-request in detail.

This will bypass the permissions dialog and prevent reuse of existing sessions during sign in and sign out. The preferPrivateSession flag is exactly what I wanted, but I did not find any resources about how to set this flag in React Native. I wonder is this flag supported at all in RN?

### Please describe a solution you'd like.

Any method to allow me setting the preferPrivateSession flag in my React Native app.

### We love contributors! Is this something you'd be interested in working on?

- [ ] 👋 I may be able to implement this feature request.
- [ ] ⚠️ This feature might incur a breaking change.

Start by searching the Authenticator React Native integration and existing references to preferPrivateSession, then compare how the option is exposed elsewhere in Amplify UI. The work is done when a React Native app can set the flag and sign-in and sign-out bypass the permissions dialog without reusing existing sessions.

Written by the indexing model from the issue text.