Added support for Sagemaker ENV variables + custom formatter scripts

[smouaa]

Description

1. Added support for following ENV variables for CX compatibility:

SAGEMAKER_MAX_REQUEST_SIZE
SAGEMAKER_NUM_MODEL_WORKERS
SAGEMAKER_DEFAULT_INVOCATIONS_ACCEPT
SAGEMAKER_MODEL_SERVER_TIMEOUT_SECONDS
SAGEMAKER_MODEL_SERVER_VMARGS
SAGEMAKER_STARTUP_TIMEOUT
SAGEMAKER_MAX_PAYLOAD_IN_MB

2. Extended custom formatters to work with existing Sagemaker scripts
3. Integration tests for CX env variables, custom formatters

SKLearn handler notebook: https://github.com/deepjavalibrary/djl-demo/blob/master/djl-serving/python-mode/sklearn_handler_guide.ipynb
XGBoost handler notebook: https://github.com/deepjavalibrary/djl-demo/blob/master/djl-serving/python-mode/xgboost_handler_guide.ipynb

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

Checklist:

• Please add the link of Integration Tests Executor run with related tests.
• Have you manually built the docker image and verify the change?
• Have you run related tests? Check how to set up the test environment here; One example would be pytest tests.py -k "TestCorrectnessLmiDist" -m "lmi_dist"
• Have you added tests that prove your fix is effective or that this feature works?
• Has code been commented, particularly in hard-to-understand areas?
• Have you made corresponding changes to the documentation?

Feature/Issue validation/testing

Please describe the Unit or Integration tests that you ran to verify your changes and relevant result summary. Provide instructions so it can be reproduced.
Please also list any relevant details for your test configuration.

• Test A
  Logs for Test A

• Test B
  Logs for Test B

[xyang16]

Do you want this to be higher priority than SERVING_XXX env? If yes, you need to move it after line 141. Otherwise SERVING_MAX_REQUEST_SIZE will override SAGEMAKER_MAX_REQUEST_SIZE.

[xyang16]

Same as above. Move after line 915 if needed.

[xyang16]

Need to move SageMakerCompatibility.applyModelCompatibility(prop) in ModelInfo.java after line 915. Because if user set entrypoint via OPTION_ENTRYPOINT env, it is not populated to properties yet.

Requested changes were implemented and approved by Xin. Merge is necessary in order to publish the container by the deadline (10/31)