[GCP] Supports GPU in Compute instances

[obierlaire]

Same approach as https://www.cloudcarbonfootprint.org/docs/methodology#graphic-processing-units-gpus

According to https://cloud.google.com/compute/docs/gpus/create-vm-with-gpus#create-new-gpu-vm , there are two ways to have a machine with GPU:

• use a machine type which has already GPU by default (a2-highgpu-* or a2-ultragpu*)
• use a standard machine type and attach GPU

So, we need to

• Regenerate data/gcp_instances.json to include list of default GPUs for instance type (should be of nvidia a100 for a2 instances)
• Add default GPU to resource when machine type has default GPU
• Add GPUs to resource when attached gpu has been declared in terraform file