Add react-native-purchases-ui

[aboedo]

📝 Why & how

Adds react-native-purchases-ui package.
RevenueCat ships the react-native-purchases and react-native-purchases-ui packages separately.
The react-native-purchases-ui package hadn't been registered before.

Note: I added this package as a separate entry. There are notes about monorepo handling in the readme but I wasn't entirely sure how to apply them, so let me know if this isn't right.

My interpretation is having a separate listing for each package with the same GitHub URL but different NPM package.

✅ Checklist

• Added library to react-native-libraries.json
• Updated library in react-native-libraries.json

• Documented in this PR how to use the feature or replicate the bug.
• Documented in this PR how you fixed or created the feature.

[aboedo]

If package is a part of monorepo, 'githubUrl' must point to directory where 'package.json' for a given package resides.

the error message is quite clear, I'll fix

[Simek]

Hello @aboedo, thanks for adding a missing entry to the directory, LGTM! 👍