Sign the image sylva-toolbox
This MR adds a digital signature to the image built by the CI.
Signature relies on cosign
and is stored in the registry.
The signing material is fetched from a sylva project leveraging cosign
- the idea could be to keep the same material for the same kind of Sylva's artefacts. This is a temporary solution waiting to be able fetching the signing material from the CI/CD variables of this project oe, better, from Vault.