Fix / Improve Caching

[lea-33]

To finally ensure the Caching works, the following steps are aquired:

• first, test the workflow with dummy numbers to ensure the functionality
  -> for that, also safe the cache locally first, and also add the respective slide images to it

• test it with a simple notebook for a few slides from different presentations

• write a function: cache(pdf, slide_number, hf_repository) that extracts the cached embeddings for each slide

• test this function and if it works, calculate all embeddings for the slides in our training materials to make them callable by this function