Start implementing upgrade status API

[andrewjstone]

Implements #8265

Still needs:

• OMDB support
• Testing

Support for artifacts other than zones will probably come in a follow up.

[plotnick]

Thanks for doing this, both the code and the output look great!

I do have one (perhaps slightly annoying) suggestion: I think we should use the term "update" everywhere instead of "upgrade". We've been somewhat inconsistent on this point in the past, but we seem to be standardizing on the former (e.g., oxide update, API endpoints under /system/update). And especially for dev/user-facing commands I think it's important to use consistent terminology so that commands and endpoints are guessable.

[andrewjstone]

Thanks for doing this, both the code and the output look great!

I do have one (perhaps slightly annoying) suggestion: I think we should use the term "update" everywhere instead of "upgrade". We've been somewhat inconsistent on this point in the past, but we seem to be standardizing on the former (e.g., oxide update, API endpoints under /system/update). And especially for dev/user-facing commands I think it's important to use consistent terminology so that commands and endpoints are guessable.

Not annoying at all! I anticipated some changes around the wording / endpoint location. @davepacheco @jgallagher Does this work for you? Any other changes you'd like to see in terms of naming?