Add sagemaker core exceptions

[benieric]

Issue #, if available:

Description of changes:

• Add exceptions.py with base SageMakerCoreError and additional static errors
• Convert all errors thrown in IntelligentDefaults flow to IntelligentDefaultErrors
• Convert all errors thrown in waiter flow to WaiterError
• IntelligentDefaultError - Raised when an error occurs in the Intelligent Defaults
  • LocalConfigNotFoundError- Raised when a configuration file is not found in local file system
  • S3ConfigNotFoundError - Raised when a configuration file is not found in S3
  • ConfigSchemaValidationError - Raised when a configuration file does not adhere to the schema
• WaiterError - Raised when an error occurs while waiting.
  • FailedStatusError - Raised when a resource enters a failed state.
  • TimeoutExceededError - Raised when a specified timeout is exceeded

NOTE: Some unrelated update and invoke tests are failing - This seperate PR fixes them: https://github.com/aws/sagemaker-core/pull/3

MOVING PR FROM PREVIOUS REPO - https://github.com/mohanasudhan/sagemaker-code-gen/pull/26

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Testing

• Added/updated unit tests

  pytest -vv tst
  black .

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