Being able to download an artifact even if default CAS backend changed #268
Description
Currently, when artifact download is invoked, the system looks for the default CAS backend and tries to find the artifact with that digest there.
The problem is that if the user performed a CAS backend change (which now they can #223), they will not be able to find previous assets, even if they have the backend registered (but not default) there.
One way we could fix this is by maintaining a lookup table between the digest and the CAS backend where the asset is, and this lookup table can be updated once the attestation is for example finished, since at that stage we have the reference of all the assets + the CAS backend used #237
Then, the download command can try to find the asset in the lookup table and load the actual CAS backend that has it, if it can't find it we could fallback to the current backend as we do today.