[Feature] Build Generation 2 Azure images to support VM sizes with A100 GPU

[r4victor]

Currently, dstack builds Generation 1 Azure VM images. But some VM sizes that we would like to support work only with Generation 2 images (e.g. NC A100 v4-series).

We need to build Generation 2 images in addition to Generation 1 images. It seems like it can be achieved with packer by using Generation 2 base image (see hashicorp/packer#8352).