add webp support to coverstore

[RayBB]

Part of #7250

Turns out with PIL webp just works. No changes needed other than allowing the format.

Unfortunately, AVIF support just isn't there yet :/
python-pillow/Pillow#7983

Technical

Testing

Upload a cover that's webp, like: https://www.gstatic.com/webp/gallery/1.webp

Screenshot

Stakeholders

@cdrini

[cdrini]

Lgtm! We tested uploading on testing, and everything seemed to work smoothly -- although note our testing environment might not be testing the entire flow, since it does just connect to prod's coverstore.

We did notice, that the original size is saved to disk as a .jpg, but the actual binary is a WEBP -- this appears to affect all non-jpg uploads, eg PNG, GIF. It doesn't seem to cause any issues, though so seems ok?

$/var/lib/openlibrary/coverstore/localdisk/2025/01/29$ ls | grep OL54067000M
OL54067000M-60P4k-L.jpg
OL54067000M-60P4k-M.jpg
OL54067000M-60P4k-S.jpg
OL54067000M-60P4k.jpg
$/var/lib/openlibrary/coverstore/localdisk/2025/01/29$ ls -al | grep OL54067000M
-rw-r--r--  1 openlibrary openlibrary   30272 Jan 29 17:27 OL54067000M-60P4k-L.jpg
-rw-r--r--  1 openlibrary openlibrary   11968 Jan 29 17:27 OL54067000M-60P4k-M.jpg
-rw-r--r--  1 openlibrary openlibrary    1602 Jan 29 17:27 OL54067000M-60P4k-S.jpg
-rw-r--r--  1 openlibrary openlibrary   57262 Jan 29 17:27 OL54067000M-60P4k.jpg
$/var/lib/openlibrary/coverstore/localdisk/2025/01/29$ head -b32 OL54067000M-60P4k.jpg
head: invalid option -- 'b'
Try 'head --help' for more information.
$/var/lib/openlibrary/coverstore/localdisk/2025/01/29$ head -c32 OL54067000M-60P4k.jpg
RIFF□□WEBPVP8X
 □□IC
 
$/var/lib/openlibrary/coverstore/localdisk/2025/01/29$ head -c32 OL54067000M-60P4k-L.jpg
□□□□JFIF□□C