276 validate reference documentation and tutorials

[M-Lampert]

This PR validates, fixes and improves the documentation:

• We make all Jupyter Tutorials run independently without file dependencies from the PathpyG repo
  • Some datasets that were only locally available(ants and email-company) are replaced by similar datasets from netzschleuder.
  • For datasets, where replacement was not possible, e.g. the synthetic dataset for the DB-GNN tutorial (docs/data/temporal_clusters.tedges), we added a snippet that automatically downloads the dataset from the repo if it is not found locally.
• Tutorial notebooks are now automatically executed during deployment and tested as part of the CI when a PR is opened.
• Code reference is updated and extended.
• Added tests for docstring examples
• All linting and static type checking errors have been fixed. The linting and static type-checking CI workflows have now been set to fail on error.