[Task] Add booking.com solution to Merlin Models example

[bschifferer]

Description

NVIDIA won the WSDM 2021 competition. As we added new features and libraries, we want to add the solution as Merlin (Models) example:
https://github.com/NVIDIA-Merlin/competitions/tree/main/WSDM_WebTour2021_Challenge/02_Models/GRU_MS_SMF

[rnyak]

@viswa-nvidia can we change the milestone to 22.10?

[bschifferer]

Radek provided an example for the new transformer architecture