Webp support

[phette23]

Description

Please describe briefly your pull request.

Adds .webp support to previewer. The previews may not look great without also telling flask-iiif to handle webp files. I added the following to my invenio.cfg and then the previews were full-size and looked as good as for other formats:

from flask_iiif.config import IIIF_FORMATS, IIIF_FORMATS_PIL_MAP
IIIF_FORMATS["webp"] = "image/webp"
IIIF_FORMATS_PIL_MAP["webp"] = "webp"

I think I will submit a parallel PR to flask-iiif with those default config changes. But this PR could be merged first without any harm and instances could always override their flask_iiif.config as above.

Edit: IIIF PR is inveniosoftware/flask-iiif#98

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

• I'm aware of the code of conduct.
• I've created logical separate commits and followed the commit message format.
• I've added relevant test cases.
• I've added relevant documentation.
• I've marked translation strings.
• I've identified the copyright holder(s) and updated copyright headers for touched files (>15 lines contributions).
• I've NOT included third-party code (copy/pasted source code or new dependencies).
  • If you have added third-party code (copy/pasted or new dependencies), please reach out to an architect.

I didn't touch any tests but didn't see ones for each image type, let me know if I missed something.

Frontend

• I've followed the CSS/JS and React guidelines.
• I've followed the web accessibility guidelines.
• I've followed the user interface guidelines.