Add additional dependencies for ModelTrainer

**Describe the feature you'd like**
When migrating from sagemaker v2 to v3, the [Estimator](https://sagemaker.readthedocs.io/en/v2.256.0/api/training/estimators.html?highlight=tensorboardoutputconfig#sagemaker.estimator.Estimator) can be replaced by ModelTrainer. However, the ~~`tensorboard_output_config`and~~ `dependencies` parameters in Estimator has no equivalent in the ModelTrainer. This functionality would be useful to have in ModelTrainer to maintain feature parity with the v2 Estimator.

**How would this feature be used? Please describe.**
* Allows the import of additional source files and dependencies into the model training container.
~~* Allows debugging visualization using TensorBoard, with customization on the location in Amazon S3 to store the output, as well as the local path in the container.~~ (addressed by [ModelTrainer.with_tensorboard_output_config](https://sagemaker.readthedocs.io/en/v2.253.1/api/training/model_trainer.html#sagemaker.modules.train.model_trainer.ModelTrainer.with_tensorboard_output_config))

**Describe alternatives you've considered**
None

**Additional context**
None

ModelTrainer のエントリーポイントから開始し、その処理を v2 Estimator の `dependencies` パラメータと比較します。追加のソースファイルと依存関係がトレーニングコンテナに入る経路を追跡し、そのうえで ModelTrainer が要求された import をサポートし、文書化されたトレーニング動作を維持していることを確認します。

索引モデルが issue の本文から書いたものです。