Update StorageSettings to use StorageDashbordFragment.

It previously was set to use the PrivateVolumeSettings. By
swapping it with the new view, we can retain the existing
behavior for external storage (PublicVolumeSettings).

This also restores the summary text to the main Settings
screen.

Bug: 34197071, 34195303
Test: Verified locally that StorageDashboardFragment is started
      instead of the PrivateVolumeSettings.

Change-Id: I5de0ea8de799d758272a1406856ae7de9b6fcc8e