Do not add "Switch user" action if switching users disallowed

Only add "Mute" action to alarm notification from background user is user switching is disallowed or disabled.

Bug: 356380324
Test: manual: 1. set timer on user 11 -> switch to another user 10 -> notification shows with 2 actions. 2. set timer on user 11 -> switch to another user 10 -> adb shell pm set-user-restriction --user 10 no_user_switch 0 -> notification shows with only "Mute" action.
Flag: android.multiuser.add_ui_for_sounds_from_background_users
Change-Id: Icbc564bb017c9ac651ba450de5c32eb83ccbecaa