have csv export template use slug for custom fields to match import

[dnoneill]

closes #2994

[taylor-steve]

Do you know if this PR will re-introduce the bug that this previous PR was addressing?

https://github.com/projectblacklight/spotlight/pull/2506/files

Just curious because this PR seems to essentially be a revert of that.

[corylown]

I think this does re-introduce the bug fixed here: #2506
(hinting at a missing test?)

Maybe the fix is to instead export the custom field slugs instead of the field name when the template is generated: ?

It's possible this was missed when we switched to prefer the slug over the full field name for sidecar data here: https://github.com/projectblacklight/spotlight/pull/2201/files

[dnoneill]

I was wondering about this. I am wondering if we want to support both. I could see instances where the solr field is preferred as well.

[dnoneill]

Decision was made to update the template download