Request: allow to use Firebase Crashlytics/Analyticts/RemoteConfig on Android library, too

## What feature would you like to see?
Just like we have a way to add Firebase Crashlytics/Analyticts/RemoteConfig, allow to also have it for Android libraries.

I was recently tasked to work on an SDK that Android developers could use via simple dependency.

For example, I need it to report via Analytics each time some function is called (no matter which app uses the SDK). Or, using Remote-config to reach some value that I've set for all SDK-users.

I ask this because all tutorials seem to be about apps. Example: https://firebase.google.com/docs/android/setup

Trying to make the new project ready for Android integration, it seems that indeed it asks for a package name, but this is something I can't provide, because it's not an app...

## How would you use it?
To know which functions are called the most, to be able to control it from afar (set which package names are allowed to use the SDK for example).
As the SDK is used for more than one application (that is its purpose), I can't set a single package name and I can't treat it as if it's a single application.
Instead I need to be more generic. Maybe for Analytics I could send the current package name, for example.

I also asked about this here:
https://stackoverflow.com/q/66622252/878126
And others have asked something similar about this here:
https://stackoverflow.com/q/38790977/878126

Start by reviewing the Android setup documentation linked in the issue and comparing how Crashlytics, Analytics, and Remote Config currently integrate with applications. Determine whether Android libraries can support these services without a single package name, and define the expected behavior for SDKs used by multiple applications before implementation.

Written by the indexing model from the issue text.