think about title of compound objects in include captions

[evanwill]

For example, https://github.com/orgs/CollectionBuilder/discussions/162

"multiple" items often don't have a title or a vague title, might need more in the caption. Consider adding parent title to the caption?
Consider if this only applies to "multiple" or if "compound_objects" get it too.

{% if captions[forloop.index0] %}{%- capture image_caption -%}{{ captions[forloop.index0] }}{% endcapture %}{% elsif figure.parentid %}{% assign parent = site.data[site.metadata] | where: "objectid", figure.parentid | first %}{% capture image_caption %}{{ parent.title }} - {{ figure.title }}{% endcapture %}{% else %}{% capture image_caption %}{{ figure.title }}{% endcapture %}{%- endif -%}