Change the first fallback sort field from title (title_sort) to component order (sort_isi) for relevance sort

Implement https://github.com/projectblacklight/arclight/issues/1585 locally for now. I'm not sure what the side-effects would be of changing the sort value for collections that is needed to implement this.

https://gitlab.oit.duke.edu/dul-its/dul-arclight/-/commit/e6b797af1004795a4f4286d4dd9f10a505269a02