cosign: OCI compliant annotations

Current annotations do not respect OCI naming rules: https://github.com/opencontainers/image-spec/blob/main/annotations.md#rules

It is not the same as https://docs.gitlab.com/user/packages/container_registry/cosign_tutorial/#example-gitlab-ciyml-configuration

Where is it coming from ???

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Also it is not configurable. I tried something but it always failed with quotes: 70948b8b