combine nodegroup stacks for easier maintenance #568

Job	Run time
build-image-neuronx	13m 55s
build-image-nvidia	4m 41s
build-image-nvidia-training	5h 1m 19s
build-image	11m 21s
build	2m 50s
build-test	1m 19s
build-image-neuron-inference	4m 32s
build-image-neuron-training	6m 5s
build-image-nvidia-inference	5h 17m 2s
	11h 3m 4s

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