Add InAppMessaging to Unity SDK

Hi,
I'm currently integrating Firebase In App Messaging in my unity aps but there is no "unity version". So i integrated manually IOS & Android SDK but :
- it's tedious (to make and maintain)
- it may be broken with firebase sdk updates
- i only partially integrate features (only what i need for now)

Firebase In App Messaging is a great feature, so every "firebase system" user may want to use it.