[Reconfigurator] Host OS update planner support

[jgallagher]

This isn't ready to merge yet; in particular, there aren't any new planner unit tests. I'm opening this now to avoid conflicting with changes @karencfv is making to the reconfigurator-cli tests (which do have updates for host OS planning on this branch).

[karencfv]

Thanks! Just a heads up that I'm changing some of the unit test structure for mgs_updates/mod.rs to account for more components here -> https://github.com/oxidecomputer/omicron/pull/8664/files#diff-7c888dfce867a1f4a2b025ee3a82410a7ef7b14785ce5a795083aa4ff148dcd9

[karencfv]

Thanks for sharing this! It shouldn't clash too terribly with what I had before d4f31f9 I'll keep a look out.

[jgallagher]

Thanks! Just a heads up that I'm changing some of the unit test structure for mgs_updates/mod.rs to account for more components here -> https://github.com/oxidecomputer/omicron/pull/8664/files#diff-7c888dfce867a1f4a2b025ee3a82410a7ef7b14785ce5a795083aa4ff148dcd9

Ahh, thanks. Honestly I'm finding the unit test stuff a little unwieldy, so I was going to take a swing at some cleanup before adding host OS unit tests. I was building off of main for that cleanup, but maybe I should build off of your branch instead?

[jgallagher]

I think this is ready for review (demo'd today on dublin!).

The diff is quite large but the vast majority is test code, and over half the diff is expectorate output. It's probably still worth reviewing that output at least at a superficial level, particularly the cmds-target-release-stdout test that walks through a whole-system update (at least up to the point of updating zones).