[feature][container] Use new cosign attestation format

[ianlewis]

The version of cosign used by the container generator (v2.2.3) is getting pretty old and should probably be updated.

The newest version of cosign (v2.5.0) includes a new attestation bundle format which we should probably support as the previous format will likely be phased out. This will also likely need a corresponding change in slsa-verifier.

[ianlewis]

We should probably also add a renovate comment and use the revovate regex manager to keep it updated.