[Conversational widget] Should scroll to bottom during streaming

[mishig25]

Conversational widgeet should scroll to bottom as streaming answer is being received. Otherwise, it creates this weird behaviour:

https://github.com/huggingface/huggingface.js/assets/11827707/e107b193-eea2-4ac5-aa54-9a303afbe594

cc: @SBrandeis @Wauplin @xenova