in addition to zstd:chunked, add support for the estargz format.
estargz is maintained at github.com/containerd/stargz-snapshotter
Images using estargz can be used on old clients and registries that
have no support for the zstd compression algorithm.
Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>
containers/image/pkg/compression depends on that function, so it's
highly undesirable for it to drag in all of containers/storage.
So, move it into a separate subpackage, along with its exclusive
dependency tree.
Code that is called both from the new pkg/chunked/compressor
and the original pkg/chunked has been moved into pkg/chunked/internal ,
so that we don't expose any new public API. That move was made
purely mechanically without any concern for conceptual consistency,
to minimize the size of the dependency (and not to spend time on
that until the concept is proven to be useful).
Signed-off-by: Miloslav Trmač <mitr@redhat.com>