Add support to programmatically add files to users / entities via RAG API

[alexrsr93]

Hi Danny & Team - new to LibreChat and loving it so far. One feature that would be super useful is to allow files to be added programatically to the RAG db. Use case is shared files across organisations / businesses, for example, lets say we have multiple Google Drive folders we'd like to be uploaded, rather than having to do each file individually, simply setting up a n8n / make workflow to add these files / sync these folders to the RAG db would be a huge timesaver / feature.