umoci v0.6.0 -- "Please mind the gap between the train and the platform."

This is a fairly major update to umoci.

This update to umoci includes support for v1.1.1 of the OCI image
specification. For the most part, this mostly involves supporting reading new
features added to the specification (such as embedded-data descriptors and
subject references used by OCI artifact images), but at the moment umoci does
not yet support creating images utilising these features.

In addition, umoci also now supports generating config.json blobs that are
compliant with v1.2.1 of the OCI runtime specification. Note that we do not
explicitly use any of the newer features, this is mostly a quality-of-life
update to move away from our ancient pinned version of the runtime-spec.

Breaking

• github.com/opencontainers/umoci/oci/config/generate.Generator has had the
  following breaking API changes made to it:
  • The existing ConfigExposedPorts and ConfigVolumes methods now return a
    sorted []string instead of a map.
  • The (Set)OS and (Set)Architecture methods have been renamed to have a
    Platform prefix (to match image-spec v1.1's organisational changes). They
    now read as (Set)PlatformOS and (Set)PlatformArchitecture respectively.

Added

• umoci stat now includes information about the manifest and configuration of
  the image, both in the regular and JSON-formatted outputs.

• umoci now has SOURCE_DATE_EPOCH support, to attempt to
  make it easier to create reproducible images. Our behaviour is modelled after
  tar --clamp-mtime, meaning that SOURCE_DATE_EPOCH will only be used to
  modify the timestamps of files newer than SOURCE_DATE_EPOCH.

  As umoci repack works based on diffs, this also means that only files that
  were modified (and will thus be usually be included in the new layer) will
  have their timestamps rewritten.

  --history.created and umoci config --created will also now default to
  SOURCE_DATE_EPOCH (if set).

  With this change, umoci should be fairly compliant with reproducible builds.
  Please let us know if you find any other problematic areas in umoci (we are
  investigating some other possible causes of instability such as Go map
  iteration).

• In order to avoid the need for a patched gomtree package
  that supports rootless mode, umoci now has a umoci raw mtree-validate
  subcommand that implements the key gomtree validate features we need for
  our integration tests.

  Note that this subcommand is not intended for wider use outside of our tests
  (and it is hidden from the help pages for a reason). Most users are probably
  better off just using gomtree.

• umoci --version now provides more information about the specification
  versions supported by the umoci binary as well as the Go version used.

• umoci config now supports specifying the architecture variant of the image
  with --platform.variant. In addition, --os and --architecture can now
  be set using --platform.os and --platform.arch respectively.

• umoci new will not automatically fill the architecture variant on ARM
  systems to match the host CPU.

Changed

• The output format of umoci stat has had some minor changes made to how
  special characters are escaped and when quoting is carried out.

Fixed

• Some minor aspects of how umoci stat would filter special characters in
  history entries have been resolved.
• umoci repack will now truncate the mtime of files added to the layer tar
  archives. Previously, we would defer to the Go stdlib's archive/tar which
  rounds to the nearest second (which is incompatible with gomtree and so in
  theory could lead to inconsistent results).
• Previously, when generating the runtime-spec config.json, umoci unpack
  would incorrectly prioritise the automatically generated annotations over
  explicitly configured labels. This precdence was the opposite of what the
  image-spec requires, and has now been resolved.

Thanks to the following contributors for making this release possible:

• Aleksa Sarai [email protected]
• Danish Prakash [email protected]

Signed-off-by: Aleksa Sarai [email protected]