[Shared] Adding mp_free_oob_enable (default: 0)

Purpose: More speedrunning features

Check in movement code that prevents it: https://github.com/ValveSoftware/source-sdk-2013/blob/0d8dceea4310fde5706b3ce1c70609d72a38efdf/mp/src/game/shared/gamemovement.cpp#L2638-L2652