Breaking: Default to traitlets based Build class

[manics]

This is a follow-up to #1518 that switches the default build class from Build to the new Traitlets based KubernetesBuildExecutor class.

[manics]

This is ready for review!

[consideRatio]

I'm not confident about this situation, but wondering if it would make practical sense to work with class state on the build class itself instead of state object instance state for this information.

If so, we wouldn't have to create a dummy object, but instead just read the relevant information from the class.

What do you think?

[consideRatio]

I suspect this relates to identifier now being made a configurable traitlet. If we go for class state, the identifier field should probably not be a traitlet - but it doesn't seem like something that makes sense for users to configure themselves, but rather like something for the creator of the buildexecutor class to declare.

[manics]

It's based on a traitlets value, which AFAIK can't be static. I've renamed the variable where it's used to make it clearer, see e38480a

[consideRatio]

If it makes sense for this to be configurable, lets go with this as it is! Can you imagine a plausible situation when this could make sense to configure?

# is this relevant/sensible to support?
c.KubernetesBuildExecutor.builder_info = <something>

I'm currently understanding builder_info as something inherent to the builder class providing it, like a __version__ field, which I don't think should be configurable. So I guess there are two parts to my question about this:

1. Should this be made configurable by using a trait with .config(True)
2. Should this be class state or object state (where I also think the use of class state prohibits the use of a trait to store it)

[manics]

For KubernetesBuildExecutor the default value includes build_image which is a user-configurable traitlet, so unless traitlets properties can be static builder_info can't be a static class property, e.g.:

{
  "builder_info": {
    "build_image": "quay.io/manics/repo2docker:2023-01-02-12-10-arm64"
  },
  "binderhub": "0.2.0+1243.gf5f8c33.dirty",
  "builder": "quay.io/manics/repo2docker:2023-01-02-12-10-arm64"
}

Compare with the current output: https://mybinder.org/versions

For config=True/False ..... debatable. /versions is a public endpoint, including on authenticated BinderHubs, so one use could be to deliberately hide the builder_info. Not sure if that's useful..... what do you prefer?

[consideRatio]

Ah, well i think its not worth further thinking if we didnt come up with a clean alternative strategy by now.

---

PR LGTM ready for merge in my mind!

Thank you for amazing efforts in binderhub Simon!!!

[consideRatio]

Thanks for amazing work @manics!!!

@minrk, since this is a breaking change, do you mind having a look also?

[consideRatio]

Thanks @manics!!! ❤️ 🎉