Add the firebase-java-sdk

**Link to project (GitHub)**: https://github.com/GitLiveApp/firebase-java-sdk

**Describe the project in 2-3 sentences**: The Firebase Java SDK is a pure java port of the [Firebase Android SDK](https://github.com/firebase/firebase-android-sdk)

**Why would Firebase developers be interested in this project?**: To use Firebase in pure java clientside environments such as [Compose Multiplatform](https://github.com/JetBrains/compose-multiplatform) desktop.

**Have you added a `.opensource/project.json` file to your site**: Yes

Examples:
- https://github.com/invertase/react-native-firebase/blob/master/.opensource/project.json
- https://github.com/sgarciac/fuego/blob/master/.opensource/project.json
- https://github.com/firebase/emberfire/blob/master/.opensource/project.json