Support History/Build configs in an immutable way

[baronfel]

I was looking towards support for scratch containers, and I reasoned that I still wanted to use the ImageConfig type to store all of the user-supplied information, but in the case of the 'scratch' image there would be no base config. Therefore some of the required properties in a configuration would need to be specified more manually. So I elevated them to first-class fields in the ImageConfig type.

As part of that, I got around to an item I've wanted to do for a while - adding a log to the History collection in the config to trace the fact that we made one of the layers.

Here's what the history of one of our generated test containers looks like when viewed under docker history <imagename>:

Docker Desktop also has a more detailed view:

[vlada-shubina]

The changes looks ok, but no tests is a concern. Do you need a hand with tests?

[vlada-shubina]

imo, with those changes on, having full model makes more sense and it looks more as it now.
However it might be easier to use ready solutions as DockerRegistryClient as discussed previously, if we need more interaction with the model.

[baronfel]

re: DockerRegistryClient

yeah, I was thinking about that and wondering how much more source-build pain we wanted to incur :)

[baronfel]

I added some tests, but then I started getting so many errors compiling in the build environment - I think because the net472 build is getting included in the unit tests in some way. That feels wrong. I am very confident in these changes with the tests, though.

[vlada-shubina]

I added some tests, but then I started getting so many errors compiling in the build environment - I think because the net472 build is getting included in the unit tests in some way. That feels wrong. I am very confident in these changes with the tests, though.

let me check it tomorrow, I think it's worth to include those tests. Feel free to merge if you need this PR earlier.

[baronfel]

Thank you @vlada-shubina for the second set of eyes! I can wait for your findings.

[vlada-shubina]

Thank you @vlada-shubina for the second set of eyes! I can wait for your findings.

had to rebase to make conflict resolution easier.
previously merged PRs included net472 build for UnitTests, but ImageConfig has to be excluded.
I made it safer by removing UnitTests from net472 build and making dependency only for net7.0, however ideally it should be gone at some point.

[baronfel]

Thanks Vlada - I agree with everything you wrote. If you're satisfied, can you approve so this can be merged?