Add option to set additional containerd configs per runtime

[elezar]

This change allows for the containerd configuration using the nvidia-ctk CLI as well as the toolkit container to set additional configuration options. This can be used, for example, to specify the value of SystemdCgroup explicitly.

For example:

./nvidia-ctk runtime configure --runtime=containerd --dry-run --runtime-config-override="{\"options\": {\"SystemdCgroup\": true}}"
INFO[0000] Config file does not exist; using empty config
version = 2

[plugins]

  [plugins."io.containerd.grpc.v1.cri"]

    [plugins."io.containerd.grpc.v1.cri".containerd]

      [plugins."io.containerd.grpc.v1.cri".containerd.runtimes]

        [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.nvidia]
          privileged_without_host_devices = false
          runtime_engine = ""
          runtime_root = ""
          runtime_type = "io.containerd.runc.v2"

          [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.nvidia.options]
            BinaryName = "/usr/bin/nvidia-container-runtime"
            SystemdCgroup = true

This can also be set using an envvar:

RUNTIME_CONFIG_OVERRIDE="{\"options\": {\"SystemdCgroup\": true}}" ./nvidia-ctk runtime configure --runtime=containerd --dry-run
INFO[0000] Config file does not exist; using empty config
version = 2

[plugins]

  [plugins."io.containerd.grpc.v1.cri"]

    [plugins."io.containerd.grpc.v1.cri".containerd]

      [plugins."io.containerd.grpc.v1.cri".containerd.runtimes]

        [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.nvidia]
          privileged_without_host_devices = false
          runtime_engine = ""
          runtime_root = ""
          runtime_type = "io.containerd.runc.v2"

          [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.nvidia.options]
            BinaryName = "/usr/bin/nvidia-container-runtime"
            SystemdCgroup = true

[shivamerla]

lgtm