Add a config to turn on window drag

This CL adds 'config_enableConnectedDisplayWindowDrag' to config.xml.

Bug: 389829585
Test: manual - disable the config and confirm multi-display code path is not used
Flag: com.android.window.flags.enable_connected_displays_window_drag
Change-Id: I2fcdef2e88005649a7279c90dad0a0989040b78a