The goal is to get rid of tezos/opam-repository. To this end, we want to use opam lock.

The steps are the following:

• unvendor everything (to simplify the next step a bit);
• have the manifest generate .opam files with all external dependencies, on which we can run opam lock to obtain .locked files;
• use those lock files in make build-*-deps;
• use those lock files in tezos/opam-repository;
• move the creation of Docker images from tezos/opam-repository to tezos/tezos.