Reconfigurator testing: Expand `target-release.txt` to walk through a full update

[jgallagher]

As of #8470, the target-release.txt reconfigurator-cli test update all the (fake) SPs and then produces a blueprint that updates one control plane zone. We should expand this to update all the zones; this will require a new reconfigurator-cli subcommand to patch sleds' zones' image sources. @sunshowers is working on this subcommand for a different set of tests; once that lands we could do this work.