Creates user_switcher_enabled setting to match setting

When the user enters UserSettings, the switch displays the setting as
on, but the setting is not created until the user modifies this for the
first time. This change makes sure that the setting is created when the
user enters UserSettings for the first time.

Fixes: 130270878
Test: manual, switch to second user and observe switcher icons.
Change-Id: I30bc5025c178da3668a76c828c34545c1d98b085