Introduce a getDatabasePath() method that enables switching storage paths

[zugaldia]

In order to enable this functionality, the developer can now set a SetStorageExternal boolean flag in the AndroidManifest.xml file to switch to external storage:

<meta-data
    android:name="com.mapbox.SetStorageExternal"
    android:value="true" />

The default value for storage remains internal storage (false), like until now.

Finally, note that this PR does not enable multiple sources for storage, tiles still need to be stored in the same database file on disk. The storage path, internal or external, is shared between the NativeMapView and the OfflineManager objects and, because it's a Manifest value, cannot be changed programmatically at runtime.

Fixes #5589.

/cc: @cammace @danswick @jfirebaugh @1ec5 @hjudge

[tobrun]

LGTM

[zugaldia]

@tobrun Thanks for the 👀 . Merged.