Currently, Fabric is supporting uploading APK to their servers and invite testers using their email to download the application.
Now, what will happen after google kill fabric mid-2019, will we be able to upload our testing apk somewhere and inv users to test it?
If it already exists on firebase please share where to do that and if not, and there's another tool to do so let us know.
firebaser here
What you're describing is a product called Crashlytics Beta.
From the Fabric roadmap:
MID 2019
Start using the next generation of Crashlytics Beta
Get valuable feedback on pre-release iOS and Android apps by using Firebase App Distribution, the new version of Crashlytics Beta, to distribute beta builds to your team.
Keep an eye out for an update on the status of Firebase App Distribution and the Fabric roadmap in the What's new in Firebase session at I/O.