[Status bar] Define status_bar_static_inout_indicators

Flag for the internalization of an external CL to define static in/out
indicators.

Bug: 310715220
Bug: 266797961
Test: systemui tests
Flag: ACONFIG com.android.systemui.status_bar_static_inout_indicators DEVELOPMENT
Change-Id: I5b82100f01fbe65f08ebb240994b4f589649d906