Launcher: use aconfig flag for bubble bar

Flag: ACONFIG com.android.wm.shell.enable_bubble_bar DISABLED
Test: make & enable / disable flag to check if it works:
      adb shell device_config put multitasking
         com.android.wm.shell.enable_bubble_bar true
Test: PlatformScenarioTests:
      android.platform.test.scenario.sysui.bubble.BubbleBarTest
Bug: 286246694
Change-Id: I0820973848675e8596e0e1605c7e43158d870382