Add resource for Backup summary.

- currently, the backup summary is using the accessibility summary
resource. In Spanish, the summary needs to be gender specific. Create
its own resource string so that it can be translated into correct
gender.

Change-Id: Iae14d7d3fc342264c5c8bff6bdfca0849bb4ba93
Fixes: 78477107
Test: make RunSettingsRoboTests