This ensures that `target.attest=["type=sbom,<value>"]` can be
appropriately merged when `--sbom=true` or `--set
target.attest=type=sbom`.
To merge, we simply naively take the last valid value.
Signed-off-by: Justin Chadwell <me@jedevc.com>
We can perform all attestation processing, handling how the sbom and
provenance arguments interact on the client, while applying defaults on
the server.
Additionally, this allows us to start pulling fields out of CommonOpts.
Signed-off-by: Justin Chadwell <me@jedevc.com>
Tonis Tiigi