E2E buildx tests

[blampe]

This adds some E2E buildx examples to showcase the proposed APIs.

An early draft of the documentation is deployed here if it would be easier for you to review in that format.

Examples were written in yaml first and converted to ts / py / java / go / cs.

Open questions:

• I'm debating changing { cacheTo: [...], cacheFrom: [...] } into { cache: { to: [...], from: [...] } but opted against it since to and from tend to be reserved keywords. I do think it's helpful to encapsulate all of the caching concerns under one object, though. Would { cache: { cacheTo: [...], cacheFrom: [...] } } be reasonable?
• I'm questioning whether there's any benefit to including manifests as an output. I'm leaning towards removing these, since the digests output is easier to access and gives you the tags you care about.
• I've made platform into an enum since there are only a few dozen platforms that we support, and it seemed useful from a validation and discoverability standpoint. I could see this being a hindrance, though, so I'm very open to rolling this back if we feel it makes things less usable.

Fixes #971

[blampe]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• E2E buildx tests #996 👈
• Support inline dockerfiles, named and remote contexts #1000
• API types for caches, exports, and platforms #993
• Multi-platform caching for buildx #981
• Handle unknown inputs and buildOnPreview #980
• Share build context hashing #962
• buildx auth #948
• buildx.Image MVP #899
• Upgrade Docker SDK #898
• Initial go-provider integration #890
• feature/buildkit

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[github-actions]

Does the PR have any schema changes?

Does the PR have any schema changes?

Looking good! No breaking changes found.

New resources:

• buildx/image.Image

Maintainer note: consult the runbook for dealing with any breaking changes.