[doc] Add docs about how to check for a session at startup

[mraible]

Describe the feature request?

Okta's quickstart guides have a "check for a session on startup" as part of its mobile guides. We'd like to add documentation on how to do this or mention that it's handled by the React Native SDK.

New or Affected Resource(s)

React Native Quickstart

Provide a documentation link

https://developer.okta.com/docs/guides/sign-into-mobile-app/react-native/main/

Additional Information?

No response