Let BackupRestoreConfirmation opt out edge-to-edge

This is a temporary solution to prevent the layout issue while
enabling the feature flag of the edge-to-edge enforcement.

We still need to make the activity handle insets properly later.

Fix: 333130113
Bug: 309578419
Flag: com.android.window.flags.enforce_edge_to_edge
Test: atest BackupEligibilityHostSideTest
Change-Id: I50f34346d70f86d92995a83dccf49a94e04f2894