fix: When pushing images to registry cache, use image-manifest=true

Without this change, when building images with --cache-to-registry,
BuildKit uses a proprietary cache artifact format, which breaks
when using third-party registries such as Harbor.

By adding the image-manifest=true option, BuildKit uses a standard
cache artifact format that is compatible with all registries.

See goharbor/harbor#18941 for background
information.

Author: fghaas

changelog.d/20241119_111602_fghaas_image_manifest.md

@@ -0,0 +1,5 @@
+- [Improvement] When building images with `tutor images build
+  --cache-to-registry`, use a cache artifact format that is
+  universally compatible with all registries. This enables the use of
+  that option when working with third-party registries such as
+  [Harbor](https://goharbor.io/).

tutor/commands/images.py

@@ -227,7 +227,7 @@ def build(
                 image_build_args.append(f"--cache-from=type=registry,ref={tag}-cache")
             if cache_to_registry:
                 image_build_args.append(
-                    f"--cache-to=type=registry,mode=max,ref={tag}-cache"
+                    f"--cache-to=type=registry,mode=max,ref={tag}-cache,image-manifest=true"
                 )
 
             # Build contexts