dockerTools.buildImage: Switch to the format image generated by Skopeo

We were using 'Combined Image JSON + Filesystem Changeset Format' [1] to
unpack and pack image and this patch switches to the format used by the registry.

We used the 'repository' file which is not generated by Skopeo when it
pulls an image. Moreover, all information of this file are also in the
manifest.json file.
We then use the manifest.json file instead of 'repository' file. Note
also the manifest.json file is required to push an image with Skopeo.

Fix #29636

[1] https://github.com/moby/moby/blob/749d90e10f989802638ae542daf54257f3bf71f2/image/spec/v1.1.md#combined-image-json--filesystem-changeset-format