Support AWS_REGION env var, cluster context fallback, and centralize boto3 client creation#395

mollyheamazon merged 2 commits intoaws:mainaws/sagemaker-hyperpod-cli:mainfrom

FarhanTejani:refactor/centralize-boto3-and-region-resolutionFarhanTejani/sagemaker-hyperpod-cli:refactor/centralize-boto3-and-region-resolutionCopy head branch name to clipboard