CI: new data bootstrapped image
The idea is that the initialization that occurs so far in all our CI jobs is lengthy and resource intensive: it accounts to about 5 minutes per job. For true installations, it makes sense to perform these steps with an initial configuration that's already as intended. But for our tests, the result is always the same for a given base image. Because the affected directories are volumes, we need to copy the result elsewhere on the filesystem, so that they aren't discarded immediately. In turn, the wrapper script used in the bootstrapped image restores them to the volumes and performs a much simpler startup sequence. The base image to use is entirely passed as an ARG, but it will typically be called by CI, perhaps with a hash-based tag.