WorkManager: iterate on the initialization process

A warning in the documentation of the library is:

> Note that on-demand initialization may delay some useful features of WorkManager such as automatic rescheduling of work following a crash and recovery from the application being force-stopped by the user or device.

```
/**
* A class that can provide the {@link Configuration} for WorkManager and allow for on-demand
* initialization of WorkManager. To do this:
*

*
• Disable {@code androidx.work.impl.WorkManagerInitializer} in your manifest

*
• Implement the {@link Configuration.Provider} interface on your
  * {@link android.app.Application} class

*
• Use {@link WorkManager#getInstance(Context)} when accessing WorkManger (NOT
  * {@link WorkManager#getInstance()})

*

* Note that on-demand initialization may delay some useful features of WorkManager such as
* automatic rescheduling of work following a crash and recovery from the application being
* force-stopped by the user or device.
*
* @see WorkManager#initialize(Context, Configuration) for manual initialization.
*/
public interface Provider {

/**
* @return The {@link Configuration} used to initialize WorkManager
*/
@NonNull Configuration getWorkManagerConfiguration();
}
```

It makes me think that we should not initialize the work manager, but let the lib do it.

Also #1012 is a thing