Add a hubverse-transform method to response to S3 object deletion triggers

[bsweger]

Background

This package's ModelOutputTransform class has a method to transform a hub's incoming model-output files to Hubverse format. ModelOutputTransform is bundled into an AWS Lambda package that is triggered whenever files are added/updated in the raw/model-output folder of a hub's S3 bucket.

The next step is ensuring that ModelOutputTransform also contains a function to delete files in a hub's S3 model-output directory if the file is removed from the hub.

Definition of done

• [ ] ModelOutputTransform contains a new method that accepts an S3 bucket name and the name of an S3 object in a hub's raw/ folder. The method uses this information to determine the corresponding "public-facing" model-output file and delete it.
• [ ] This new method should issue a warning if the object has already been deleted, but should not fail.
• [ ] lambda_function.py is updated to invoke the new deletion method when it's triggered by an s3:ObjectRemoved:* S3 event.

This issue to to create the

[bsweger]

Discussed this with @matthewcornell, and we decided that the delete method does indeed belong in the ModelOutputTransform class (instead of a new class) because there's some shared code, and the delete operation is simple.

We did decide to split the new delete code into separate unit test files, however, since the existing test_model_output.py is getting long-ish.