feat: Support placeholders for TrainingStep

Description

Add support to define Training parameters dynamically using placeholders in TrainingStep

Fixes #138, #39 and #42

Why is the change necessary?

Currently, it is not possible to use placeholders for Sagemaker Training properties. The properties cannot be defined dynamically, as they need to be defined in the Estimator which does not accept placeholders. This change makes it possible to use placeholders for Training properties by using the parameters field that are passed down from the TrainingStep.

This addresses 3 issues:

138: Setting the Environment variables for TrainingStep will be possible by providing those variables in the parameters argument (See CreateTrainingJob request for more details)
39: Using a different input s3 location will be possible by using placeholders such as ExecutionInput to define the InputDataConfig in the parameters argument.
42: Setting EnableManagedSpotTraining will be possible by defining that parameter in the TrainingStep parameters argument (see [See CreateTrainingJob request)

Solution

Use the parameters field that is compatible with placeholders to define TrainingStep properties. Merge the parameters that were generated from the Estimator with the input parameters:

The input parameters will overwrite the parameters generated from the Estimator if the properties were defined in both
All TrainingStep properties will be placeholder compatible except for data - which requires RecordSets as data depending on the estimator used to define the tuner.
The input parameters should follow the schema described in CreateTrainingJob API doc
Same solution was adopted for feat: Support placeholders for processing step

Testing

Added unit and integration tests

Pull Request Checklist

Please check all boxes (including N/A items)

Testing

[X] Unit tests added
[X] Integration test added
[X] Manual testing - why was it necessary? could it be automated? - N/A

Documentation

[X] docs: All relevant docs updated
[X] docstrings: All public APIs documented

Title and description

[X] Change type: Title is prefixed with change type: and follows conventional commits
[X] References: Indicate issues fixed via: Fixes #xxx

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license.

aws / aws-step-functions-data-science-sdk-python