feat: add customer examples for invoice pdf and medical report image

[jojortz]

Feature
Add new demos:

• pdf_to_key_value.ipynb and async_pdf_to_key_value.ipynb: Demo extracting key-value from example Invoice document
• image_to_key_value.ipynb and async_image_to_key_value.ipynb: Demo extracting key-value pairs from example medical report image

Testing

• ran automated tests in test/test.py via pre-commit
• ran new notebooks

[CambioML]

Please fix broken test cases.

[CambioML]

Please fix broken test cases.

[CambioML]

You should consider to put sensitive information even this in a S3 bucket and put a .env to ask people to put access key and secret key to download.

[CambioML]

Is this issue addressed?

[CambioML]

Please fix broken test cases.

What is the status of the broken unittest?

[jojortz]

All test cases passed.

This is already updated to be extract_key_value to match cambio-core.

TODO
Once the new extract_key_value is pushed to public, this will need to be updated as the output format has changed with cambio-core

[lingjiekong]

LGTM.