Draft an integration of TGI with Jetstream/pytorch

[tengomucho]

Jetstream is a very performant solution for inference for TPUs. The idea is to use their Pytorch implementation and try to use it as backend for TGI.
If the solution is successful, it could eventually replace current optimum-tpu TGI, and the code might land directly as part of TGI.
Note that this will require the models obtained from #58.

[tengomucho]

This is being done in #88