previewer not showing images (change in image key format)

[dfdan]

Package version (if known): v1.1.1

Describe the bug

iiif_image previewer can not show images due to incorrect image keys from utils.py/iiif_image_key()

Steps to Reproduce

(tested on RDM 4)

1. add to invenio.cfg to enable IIIF Image service -

IIIF_IMAGE_OPENER_HANDLER = "invenio_rdm_records.resources.iiif:image_opener"
IIIF_API_DECORATOR_HANDLER = None
PREVIEWER_PREFERENCE=['iiif_image']; 
IIIF_PREVIEW_TEMPLATE = 'invenio_app_rdm/records/iiif_preview.html'

2. At this point, manually constructed image URLs will work, however...
3. preview a record with attached image
4. error thrown in previewer iframe

  ...
  File "/home/blip/npg0/invenio-iiif/invenio_iiif/utils.py", line 29, in iiif_image_key
    bucket_id = obj.get('bucket')
AttributeError: 'FileItem' object has no attribute 'get'

As this function is now being passed an unexpected datatype.

Expected behavior

image should be loaded in previewer.

Additional context

Although this function is only used internally, it would be useful for things (eg an IIIF presentation seralizer) to be able to get the keys / image API URLs from invenio-iiif.

I will link a quick local fix I've implemented in a moment, but @lnielsen / @ppanero can we talk about how I could implement a more general fix so invenio-iiif can get the key from the records resources without making invenio-iiif dependent on rdm-records?