Backport pull request #12490 from jellyfin/release-10.9.z

Set Content-Disposition header to attachment for image endpoints

Original-merge: 9645955629

Merged-by: crobibero <cody@robibe.ro>

Backported-by: Joshua M. Boniface <joshua@boniface.me>

Jellyfin.Api/Controllers/PluginsController.cs

@@ -233,6 +233,8 @@ public class PluginsController : BaseJellyfinApiController
             return NotFound();
         }
 
+        Response.Headers.ContentDisposition = "attachment";
+
         imagePath = Path.Combine(plugin.Path, plugin.Manifest.ImagePath);
         return PhysicalFile(imagePath, MimeTypes.GetMimeType(imagePath));
     }