New handler added to allow the deletion of the generated files.

[luismanez]

Added a new Handler that allows the deletion of the generated "physical" (disk, blob...) files after a document has been imported.

Motivation and Context (Why the change? What's the scenario?)

This should address this question: https://github.com/microsoft/kernel-memory/issues/107

High level description (Approach, Design)

This new handler as not been added to any default pipeline, so nothing changes for current clients. However, the Handler is not present, so it can be passed as step when calling any of the current ```ImportDocumentAsync````
i.e:

await memory.ImportDocumentAsync(
    "sample-Wikipedia-Moon.txt",
    steps: new[] { Constants.DeleteDocumentGeneratedFilesPipelineStepName });

@dluc this solution would give us the functionality we need, as would avoid any compliance issue with having enterprise docs out of M365. It's not a perfect solution, and I'm happy to make any changes if providing guidance.
Note: There's still the pipeline_status.json file, but that's ok for us, and can be addressed with a container policy.

Thanks.

[dluc]

looking into it, stay tuned :-)