Use separate Settings entry to hide Private space entry point in All Apps

Private space settings page is newly added for Private Space feature. This page has a toggle switch with which user should be able to control hide/unhide private space entry point in All Apps.
Launcher will read this setting to hide/unhide the entry point.

Bug: 302682054
Test: unit+manual
Change-Id: I43bacd25ab3848202a93d8f032dd469520d13a22