[FIX] ir_http: use meaningful ETag for images (#20283)

After setting the image on a product variant, the controller for `/web/image`
incorrectly returns the code 304 - Not Modified.  This bug occurs because
 1. the response ETag is a hash of the **last modified date** of the record;
 2. the record is actually **not** updated in that case, because
     - the image field is a non-stored computed field, and
     - its inverse method only modifies the variant's template.

Fix the issue by making the response ETag a hash of the **content**, which is
read by the controller anyway.

OPW 769302

0 files changed, 0 insertions, 0 deletions