Add device config for experiment of ignoring activity orientation

With command:
 adb shell device_config put window_manager \
     ignore_activity_orientation_request true
Activity's orientation will be always "unspecified".

Flag: EXEMPT disabled code
Test: presubmit
Bug: 357141415
Change-Id: Ib84af6637fca45323c3064ca92e715dcd1c7040f