Use the same command as the Cookbook README for Redox OS APT key retrieval.
Keep adding the Redox OS repository in a dedicated file. This allows updating it specifically without updating the other repositories one more time.
Prepare user environment at build time and update user and group id at runtime if necessary.
Update submodule sync step to avoid a dependency on cargo
Run `make update all` instead of just `make all`. The target `update` didn't update the container environment since it was executed on the host.
