Possibility to add source_directory to Sagemaker.processing.ScriptProcessor

**Describe the feature you'd like**
Currently there is no option to add source_dir to `Sagemaker.processing.ScriptProcessor`, which makes it difficult to have modular code.

**How would this feature be used? Please describe.**
This will help using ScriptProcessor to be used for running complex processing logic. Especially where the project has different modules and each module perform different processing step.

**Describe alternatives you've considered**
running it directly on docker ?

首先定位 Sagemaker.processing.ScriptProcessor 入口点，并检查它当前如何打包或公开 processing scripts。确定模块化 processing code 所需的 source_directory 行为，然后为该行为添加 coverage，并验证 ScriptProcessor 能够运行组织在多个模块中的 code。

由索引模型根据 Issue 内容生成。