Add React Native metrics and logs onboarding instructions

[christophaigner]

React Native metrics and logs onboarding screens are missing setup instructions.

For metrics, the React Native SDK already has documentation at https://docs.sentry.io/platforms/react-native/metrics/, but the in-product "Getting started with metrics" page still shows React Native in the list of upcoming SDK support. The metrics onboarding empty state should be updated to include React Native instructions and React Native should be removed from the upcoming SDKs list.

For logs, the logs onboarding checklist for a React Native project is empty, while frameworks like Next.js show a full setup checklist. The React Native logs onboarding should be updated to provide equivalent setup steps.

[linear]

RN-477