Grant storage permission to the content capture service.

This unblocks dogfooding of go/image-aware-sharesheet. The feature is currently experimental, so the change will be rolled back if it doesn't graduate to production before R is cut (tracked in b/143339485).

Bug: 147206065
Test: dumpsys package
Change-Id: If960a412cb5f603348e99b1878897147caf3a1f5