GPU-aware MPI selector

[luraess]

Addresses #63

EDIT:

The architecture constructor Arch() has now an extra kwarg gpu_aware which allows to specify whether the target MPI implementation is GPU-aware when initialising a distributed architecture. GPU-awareness defaults to false for CPU() and Metal() backends:

Architectures.Arch(backend::Backend, comm::MPI.Comm, dims; device_id=nothing, gpu_aware=true)

[luraess]

Needs a final checkup on ALPS and LUMI to make sure we would be good to go.

[luraess]

@utkinis this went under during rework of #65

[luraess]

Testing on ALPS:

• with CUDA-aware MPI (and default arch -> gpu_aware=true)
  

• without CUDA-aware MPI and gpu_aware=false
  

[luraess]

This could be ready for review. Then we need to release a patch (0.1.24) to prop the bug fix from #85 (comment)

[utkinis]

Thanks @luraess, looks good to me