c8d/snapshot: Create any platform if not specified

With containerd snapshotters enabled `docker run` currently fails when
creating a container from an image that doesn't have the default host
platform without an explicit `--platform` selection:

```
$ docker run image:amd64
Unable to find image 'asdf:amd64' locally
docker: Error response from daemon: pull access denied for asdf, repository does not exist or may require 'docker login'.
See 'docker run --help'.
```

This is confusing and the graphdriver behavior is much better here,
because it runs whatever platform the image has, but prints a warning:

```
$ docker run image:amd64
WARNING: The requested image's platform (linux/amd64) does not match the detected host platform (linux/arm64/v8) and no specific platform was requested
```

This commits changes the containerd snapshotter behavior to be the same
as the graphdriver. This doesn't affect container creation when platform
is specified explicitly.

```
$ docker run --rm --platform linux/arm64 asdf:amd64
Unable to find image 'asdf:amd64' locally
docker: Error response from daemon: pull access denied for asdf, repository does not exist or may require 'docker login'.
See 'docker run --help'.
```

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

daemon/containerd/image_snapshot.go

@@ -28,7 +28,7 @@ func (i *ImageService) PrepareSnapshot(ctx context.Context, id string, parentIma
 
 		cs := i.client.ContentStore()
 
-		matcher := platforms.Default()
+		matcher := matchAllWithPreference(platforms.Default())
 		if platform != nil {
 			matcher = platforms.Only(*platform)
 		}