Separate string config for ignore_orientation_request

As recommended in cr/700626301, splitting into a separate device_config
namespace to take away the risk of reassigning a bool flag to a string
flag on the server side experiments platofmr.

This allows completely separate studies on the all screens and large
screens features.

Bug: 357141415
Test: atest ActivityRecordTests
Flag: EXEMPT adds experiment configuration (off by default)
Change-Id: I0a9dea6796f39643451ce3a96d147954686b1afe