Interactive ingestion options for Easy RAG

[jmartisk]

At the Brno JUG meeting, there was a suggestion to allow easier experimenting with RAG in the sense of automatically ingesting files that get added to Easy RAG's document directory over time in Dev Mode, without triggering a reload.

~I'm not sure if Dev mode supports watching a whole directory for new files though~ -> actually we would probably have to watch the directory in some custom way in order to NOT trigger a reload

Another interesting option to explore would be allowing to 'upload' a new file into the embedding store via the Dev UI.