🌱 use GitHub Actions to build an image usable for Prow jobs

[embik]

This is the third time I'm trying to make Prow merge my PR (previously: #35 and #34).

This PR is a follow-up to the discussion in Slack regarding the CI job base image.

I've tried my hands at creating a simple version of a build image that ships with Go 1.19.9 and kubectl 1.26.3 and is built via GitHub Actions, since kcp images are currently published as GitHub Packages. I'm very very new to GitHub Actions, so I hope what I built here makes sense. It might not be the way to go for us, so this is open to discussions.

[embik]

/cc @xrstf

[kcp-ci-bot]

Hi @embik. Thanks for your PR.

I'm waiting for a kcp-dev member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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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.

[xrstf]

/ok-to-test

[xrstf]

/approve /lgtm

[kcp-ci-bot]

LGTM label has been added.

Git tree hash: 0ebc085662cf6065d4c35ea3595c58a0e768216b

[kcp-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: xrstf

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/kcp-dev/infra/blob/main/OWNERS)~~ [xrstf] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[xrstf]

So after debugging this for a long time, trying all sorts of things, it seems that there are just some bugs (?) in github (?) and/or prow (?) that prevent PRs from getting merged under certain conditions.

We are apparently not the first to experience this, as @nikhita found out on k8s slack:

• https://kubernetes.slack.com/archives/CDECRSC5U/p1667474242076159?thread_ts=1667223444.882849&cid=CDECRSC5U
• https://kubernetes.slack.com/archives/CDECRSC5U/p1671121791659919?thread_ts=1653297447.079519&cid=CDECRSC5U

It seems to be related to the fact that this PR modifies .github/.

Hoping that the problem will not happen again with future PRs that only modify and not add new stuff to .github/, let's merge this and :crossed_fingers: