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 ?

Start by locating the Sagemaker.processing.ScriptProcessor entry point and reviewing how it currently packages or exposes processing scripts. Determine the expected source_directory behavior for modular processing code, then add coverage for that behavior and verify that ScriptProcessor can run code organized across modules.

Scritto dal modello di indicizzazione a partire dal testo della issue.