Respect default_bucket_prefix by default for Estimator code_location

**Describe the feature you'd like**
Currently the `code_location` attribute of the Estimator class defaults to using the `output_bucket` parameter [docs link](https://sagemaker.readthedocs.io/en/stable/api/training/estimators.html#sagemaker.estimator.EstimatorBase):

> If not specified, the default code location is ‘s3://output_bucket/job-name/’.

The [Session object also has a parameter](https://sagemaker.readthedocs.io/en/stable/api/utility/session.html#sagemaker.session.Session) `default_bucket_prefix` that can be configured.

Ideally, if
1. The `output_bucket` part of `output_path` is the `default_bucket`
2. `_is_output_path_set_from_default_bucket_and_prefix` is False

Then the default location should respect both the `default_bucket` as well as the `default_bucket_prefix`.

e.g. `s3://default_bucket/default_bucket_prefix/job-name/`

This change would be implemented in [_stage_user_code_in_s3](https://github.com/aws/sagemaker-python-sdk/blob/23109671f6262269ab54cdd9aeb5ebe4ea640d25/src/sagemaker/estimator.py#L1042).

Otherwise, the default behavior creates artifacts at the root of the bucket. This means that default behavior for environments where IAM bucket write access is limited by prefix (i.e. SageMaker Unified Studio) will fail.

**How would this feature be used? Please describe.**
If this behavior is implemented, model code assets would be uploaded by default to a prefix where write access is allowed.

**Describe alternatives you've considered**
Currently `code_location` needs to be manually configured to work in SageMaker Unified Studio. This is poorly documented as part of features like [ModelStep](https://sagemaker.readthedocs.io/en/stable/workflows/pipelines/sagemaker.workflow.pipelines.html#sagemaker.workflow.model_step.ModelStep) where it needs to be configured in `repack_model_step_settings` as the model.register output populates `output_path` by default in a pipeline.

If this change cannot be implemented in code, explicit documentation should be provided about configuring parameters to output code in the SageMaker Unified Studio project prefix.

src/sagemaker/estimator.py の _stage_user_code_in_s3 から始め、リンクされている Estimator と Session のドキュメント、および ModelStep/repack_model_step_settings の参照を確認します。出力パスについて記載された条件下で、デフォルトのコードの場所が default_bucket_prefix を使用し、コードの変更が不可能な場合は設定方法がドキュメント化されていれば完了です。

索引モデルが issue の本文から書いたものです。