Unable to choose what image attribute to use

[Florkin]

We work on a website where "small_images" attribute is unused. So, indexation don't find images URL, and records only placeholders.

[Florkin]

I will submit a merge request soon to allow configuring this field.

[Florkin]

As some website like our client's uses custom image management, I think we should be able to override or plugin getImageUrl() method. For that it must be public.
I updated the PR