Add CSV/TSV support with row-aware chunking

[peymanvahidi]

Currently, DocumentReader only supports .pdf and .txt files, it's good to have .csv/.tsv tabular file support for RAG ingestion.

[slobentanzer]

@peymanvahidi thanks, good point. We'll need to check if there's a more modern library for ingestion now, maybe we can save / outsource some effort. There must be a lot of developments in that space since we created it.