Add compatibility-version 30 for the new OCI media type default while keeping
version 20 pinned to the historical image exporter behavior through v0.31.x.
Track omitted oci-mediatypes separately from explicit false, add v30
compatibility goldens, and document the supported compatibility versions.
Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
Add solve-wide compatibility-version support for image and oci
exports, with historical goldens and release compatibility tests.
Backfill version 10 for v0.13-v0.14 git artifact behavior, keep
version 20 as current, and reject unsupported zstd on v10.
Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
