text: Title: DocumentSplitter with NLTK download breaks AWS Lambda deployments
  Body: **Describe the bug**
  #8755 mentions that `DocumentSplitter` argument `split_by='sentence'` now uses NLTK. When running in AWS Lambda with an updated Haystack (2.8.0 -> 2.9.0) which includes this change, the lambda exits with an error as it cannot download some NLTK files. AWS Lambda deployments have a read-only filesystem, the updated `DocumentSplitter` now triggers download of some NLTK files causing the AWS Lambda to fail.
  
  Is there a way to download these NLTK files ahead of time, i.e., during docker build of AWS Lambda image, so they do not need to be downloaded at runtime?
  
  **Error message**
  ```txt
  [nltk_data] Downloading package punkt_tab to
  [nltk_data] /home/sbx_user1051/nltk_data...
  [Errno 30] Read-only file system: '/home/sbx_user1051'
  ```
  
  **Expected behavior**
  Updating Haystack from one minor release to another will not result in otherwise unchanged code breaking due to changes in the Haystack API.
  
  **System:**
   - OS: AWS Lambda
   - Haystack version (commit or version number): 2.9.0
  