Add Thumbnail to OAI Feed

[christhepianist]

Descriptive summary

We are running Hyku version 6 with all main commits through 920da19.

We have a request from a state library that is harvest by DPLA to include the item thumbnail in the OAI feed.

Rationale

The DPLA collection normally includes thumbnails for the items in their collections so patron can view a small version before clicking through to the library's repository page to see the item itself.

Expected behavior

The OAI feed includes the item-level thumbnail.

Actual behavior

The current implementation of the OAI feed does not include the thumbnail.

Steps to reproduce the behavior

1. Find a collection URL, e.g., https://zinnia.dlf2024.hyku.amigos.org/
2. Append "catalog/oai" to the end of the URL, e.g., https://zinnia.dlf20204.hyku.amigos.org/catalog/oai
3. Look at the feed to see that the thumbnail is included

Related work

Link to related tickets or prior related work here.
ATLA has implemented this change. They sent us this information that might be helpful: