[ENHANCEMENT] Improve ImageField error messaging to deal with paths, urls, none

[cceyda]

Is your feature request related to a problem? Please describe. I'm already hosting my images independently. I don't wanna save he image inside the argilla dataset just the url... there currently doesn't seem to be a way to do this using ImageField (I was hoping this was what was meant by image support but ended up having to rollback to markdown hack again)

Describe the solution you'd like ImageField should support urls

Describe alternatives you've considered Use markdown

Additional context