SF: Add a readonly feature flag for display config error HAL changes

Bug: 374184110
Test: adb shell dumpsys SurfaceFlinger | grep display_config_error_hal
-- Verify that the flag shows up
Flag: com.android.graphics.surfaceflinger.flags.display_config_error_hal

Change-Id: I78af63115914c8ae53dbb04f6d86f601e502ec8f
Signed-off-by: Manasi Navare <navaremanasi@google.com>