Feat/contain nltk assets in docker image

[christinestraub]

This pull request adds NLTK data to the Docker image by pre-packaging the data to ensure a more reliable and efficient deployment process, as the required NLTK resources are readily available within the container.

• Modified the Dockerfile to include a stage for downloading and installing NLTK data.
• Updated the Dockerfile to copy the downloaded NLTK data into the appropriate directory within the container.
• Adjusted the application setup to verify the presence of NLTK assets during the container build process.