`kms_key` in `sagemaker.processing.Processor` should default to `output_kms_key`

[admivsn]

Describe the bug
The kms_key used to encrypt either the user code file or local inputs when uploading to S3 should default to output_kms_key.

This would align the behaviour of with sagemaker.estimator.Estimator where output_kms_key is used to encrypt the tar'd user training code when uploading to S3.

Also, since output_kms_key is resolved from the config it means that kms_key can inherit this default from the config.

To reproduce
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Expected behavior
The kms_key should default to output_kms_key. This can be implemented in either:

• sagemaker.processing.Processor._normalize_args
• sagemaker.processing.Processor._normalize_inputs

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System information
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• SageMaker Python SDK version: v2.232.0
• Framework name (eg. PyTorch) or algorithm (eg. KMeans): N/A
• Framework version: N/A
• Python version: 3.10
• CPU or GPU: CPU
• Custom Docker image (Y/N): N/A

Additional context
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[cylaceste]

This is well-thought out! My thoughts are: output_kms_key being applied to the input code doesn't quite make sense from a naming perspective.

And in the estimator case, it's only when the buckets are the same (output and code) that it's applied.

kms_key = self.output_kms_key if code_bucket == output_bucket else None

Probably because it's generally safe to assume if the bucket is the same and the output has some encryption, the same encryption can be applied to the code, whereas not applying it to the code might not work for uploading due to bucket policies. Maybe this logic was added as a fix to get around some common user errors caused by bucket encryption policies.

Actually it might make sense for the estimator to encrypt the code with a kms_key that is not the output_kms_key.