Container images used for Build/CI/CD

[achamayou]

In #6270, we moved the storage of images to GHCR, and added attestation. We mostly kept the current naming/tagging scheme however, as follows:

ccf/ci:build-YYYY-MM-DD-sgx
ccf/ci:build-YYYY-MM-DD-snp-clang15
ccf/ci:build-YYYY-MM-DD-virtual-clang15

There are some issues with this:

1. snp and virtual are identical now. We also don't need the compiler name in the tag anymore, or beyond short transition periods in the future.
2. Attestations talk about a (subject name, subject digest), where the subject name is the image, there is no room for additional metadata, such as the platform or the tag. This means that there is no way to tell from an attestation which platform the build was for unless the platform is captured in the image name.
3. We can't use the latest tag.

If we move the platform from the tag to the image name, we could solve 2. and 3. (and do 1. along the way since we're switching), for example:

ccf/ci:build-YYYY-MM-DD
ccf/ci-sgx:build-YYYY-MM-DD

This amounts to rolling back some of the change that was done in #3839. Unfortunately the link to the naming policy is now dead, and I cannot find a replacement. Should we want to stay with / as the only delimiter, we could do:

ccf/ci/default:build-YYYY-MM-DD
ccf/ci/sgx:build-YYYY-MM-DD

What do we think?

[achamayou]

Done in #6281

We now have:

https://github.com/orgs/microsoft/packages/container/package/ccf%2Fci%2Fsgx
https://github.com/orgs/microsoft/packages/container/package/ccf%2Fci%2Fdefault