Use collection_id for linking rather than inferring from eadid

[corylown]

At the last community call (2024-04-22) we discussion a desired feature to make it easier to customize the formation of the collection document id. The use cases cited were needing to add the repository name/code to prevent identifier collisions across repositories and adding a slug version of the title to the id for friendlier URLs.

As I was looking at how we could better support this I found that there were a couple places in the application where we were inferring the parent collection id from the normalized form of the eadid. I found this confusing and was concerned that allowing customization of the document id would break these assumptions about the relationship between the parent collection document id and the eadid.

This PR attempts to remove this assumption from the app so we can (in a future PR) add a seam for customizing the collection document id formation.

Instead of inferring the parent collection document id from the eadid this creates a SolrDocument accessor method collection_id using the _root_ Solr field from Solr's nested document structure. This change works with either older style legacy_id parent field relationships or the newer parent_ids field. It should be completely backwards compatible with existing arclight v1 apps.

Grateful for feedback, questions, concerns.