Handle arrays for metadata['description'] in addMetadata()

[hadro]

Flagged by @barmintor on the IIIF community call:

Want to flag this - working: https://iiif.archive.org/iiif/2/annualreport00carn_14/manifest.json
broken: https://iiif.archive.org/iiif/3/annualreport00carn_14/manifest.json

At a quick glance, looks like it's failing because metadata['description'] is an array: https://archive.org/metadata/annualreport00carn_14

[hadro]

The fix here is pretty simple, we need to make another use of the existing coerce_list() function to handle complexity in description fields.

Specifically,

Line 304:
item.summary = {"none": [metadata["description"]]}
should be:
item.summary = {"none": [coerce_list(metadata["description"])]}

and similarly Line 108:
child.summary = {"none": [item['description']]}
should be:
child.summary = {"none": [coerce_list(item["description"])]}

@digitaldogsbody CCing you again here, if you're making changes soon feel free to incorporate but if not I can do a PR in the coming days

[digitaldogsbody]

For documentation purposes - I actually went with a slightly different fix here: Since summary is a language map (https://iiif.io/api/presentation/3.0/#summary), it can have an array of values, and the issue was that we were double-wrapping it so it became "summary": {"none": [["value 1", "value 2"]]}.

I've fixed it by adding a conditional that only wraps the value in a list if it isn't already, otherwise it passes it through as-is.