[enhancement] Move the code generator logic to a dockerfile

[alias-rahil]

Why?

Based on the current open issues, lots of users are having a hard time making the code generation script to work correctly for their projects. The current implementation is a bash script that heavily depends on:

1. go envs should be correctly populated to shell
2. location of the codebase should be $GOPATH/src/github.com/kubernetes/sample-controller
3. maintaining a vendor directory, if using go modules

How?

Docker supports exporting build artifacts to the host machine via buildkit. We can leverage this feature. This will also make verifying codegen in CI pipelines very easy. Sample dockerfile:

# hack/Dockerfile.update-codegen

# Usage: docker buildx build --file hack/Dockerfile.update-codegen -o . .

FROM golang:1.17 AS build
WORKDIR /go/src/github.com/kubernetes/sample-controller
RUN go get k8s.io/code-generator@v0.23.4
COPY . .
RUN bash /go/pkg/mod/k8s.io/code-generator@v0.23.4/generate-groups.sh all \
    github.com/kubernetes/sample-controller/pkg/generated github.com/kubernetes/sample-controller/pkg/apis samplecontroller:v1alpha1 \
    --go-header-file /go/pkg/mod/k8s.io/code-generator@v0.23.4/hack/boilerplate.go.txt

FROM scratch
COPY --from=build /go/src/github.com/kubernetes/sample-controller/pkg pkg

I would be happy to make a PR or give more clarity on the idea if required.

[k8s-triage-robot]

The Kubernetes project currently lacks enough contributors to adequately respond to all issues and PRs.

This bot triages issues and PRs according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
• After 30d of inactivity since lifecycle/stale was applied, lifecycle/rotten is applied
• After 30d of inactivity since lifecycle/rotten was applied, the issue is closed

You can:

• Mark this issue or PR as fresh with /remove-lifecycle stale
• Mark this issue or PR as rotten with /lifecycle rotten
• Close this issue or PR with /close
• Offer to help out with Issue Triage

Please send feedback to sig-contributor-experience at kubernetes/community.

/lifecycle stale

[k8s-ci-robot]

@alias-rahil: Closing this issue.

In response to [this](https://github.com/kubernetes/sample-controller/issues/85#issuecomment-1154942998): >/close Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes/test-infra](https://github.com/kubernetes/test-infra/issues/new?title=Prow%20issue:) repository.