add option for input warping in non-linear fully Bayesian GPs (#2858)

Summary:
Pull Request resolved: #2858

X-link: facebook/Ax#3810

see title.

Reviewed By: Balandat

Differential Revision: D74826655

fbshipit-source-id: c9097d557ee8d07956128599929ad8f8e7521c89

Author: sdaulton