Migrate setup.py to modern pyproject.toml and allow import using sagemaker_core namespace

[benieric]

Issue #, if available:

Description of changes:

• Migrated project configuration from setup.py to pyproject.toml for better build system isolation as per PEP 518.
  • https://pip.pypa.io/en/latest/reference/build-system/pyproject-toml/
• Fixed imports namespace to allow all modules under src to be imported using 'sagemaker_core' as the module name.
  • Add move all files under src/ to src/sagemaker_core
  • https://packaging.python.org/en/latest/guides/packaging-namespace-packages/

Testing

!python -m build
!pip install dist/sagemaker_core-0.1.0.tar.gz

from sagemaker_core.generated.resources import TrainingJob
for job in TrainingJob.get_all():
    print(job.training_job_name)

• can import using sagemaker_core module namespace

VS Before

from src.generated.resource import TrainingJob

• need to import using src

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