Add OCR notebooks for synchronous and asynchronous processing

[ffeldhaus]

In this PR notebooks for synchronous and asynchronous processing are added. They contain generic wrapper functions for Document AI process and batch_process which do some pre-checks on the documents and simplify inputting documents.

As part of the PR the requirements.txt has been updated to use the latest document AI package and some additional packages required for document pre-checks and displaying OCR results. All code uses the v1 (GA) endpoint of Document AI.