chore: pass contentContainerStyle to MessageFlashList

[normanwilde]

🎯 Goal

This PR enables passing additionalFlashListProps.contentContainerStyle to the <MessageFlashList /> component similar to how it works on <MessageList />.

🛠 Implementation details

Extends flatListContentContainerStyle with additionalFlashListProps?.contentContainerStyle.

🎨 UI Changes

n/a

🧪 Testing

Pass the following as additionalFlashListProps to <MessageFlashList />:

{
  contentContainerStyle: {
backgroundColor: "blue",
  },
}

☑️ Checklist

• I have signed the Stream CLA (required)
• PR targets the develop branch
• Documentation is updated
• New code is tested in main example apps, including all possible scenarios
  • SampleApp iOS and Android
  • Expo iOS and Android