Metadata fields configuration should give some indication of the underlying solr field

[cbeer]

It is confusing when some of the metadata fields share the same label (e.g. "Date" in exhibits.stanford.edu). It would use useful to have some user-facing way to discover which field is actually being referred to (and/or discover the original name of the field)

[corylown]

Relates to https://github.com/sul-dlss/exhibits/issues/2356