[SageMaker] Use SageMaker local mode to launch SageMaker jobs locally, remove custom Docker compose instructions.

[thvasilo]

Issue #, if available:

Description of changes:

• Add instructions and support to launch SageMaker jobs locally use SageMaker's own local mode, instead of the customer Docker compose solution.
• Instead of having to mess with Docker compose, users are now able to test multi-instance SageMaker jobs locally, just by providing instance-type local to the launch script(s).
• This should make it easier to test features that require distributed execution
  • Devs can build an image locally, and provide e.g. --image-uri graphstorm:sagemaker-cpu --instance-type localto the launcher. This will launch local jobs with containers using the local image.
• NOTE: We do not support local GSProcessing SageMaker jobs.

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