chore(helm): Switch to official registry for kubectl image by default

[fhoekstra]

Motivation

Bitnami does not maintain their images anymore and they will soon be taken offline: we need to switch the default kubectl image for this Helm chart to a maintained registry that will continue to be available for pulls.
Source: bitnami/containers#83267

The official k8s registry seems like the best place to get a kubectl image.

There is one added maintenance burden though: the k8s registry does not keep a latest or release tag, so we'll have to keep this image tag up-to-date with recent patches.

If you are interested, I could help with configuring Renovate for this repository to keep this image tag up to date with patches automatically.

Important items to consider before making a Pull Request

Please check items PR complies to:

• All commits in the PR are squashed. More info
• The PR is made into dedicated next-release branch, not into master branch¹. More info
• The PR is signed. More info

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¹ If you feel your PR does not affect any Go-code or any testable functionality (for example, PR contains docs only or supplementary materials), PR can be made into master branch, but it has to be confirmed by project's maintainer.

[fhoekstra]

@Slach according to my testing, the official kubectl image has no /bin/sh, it only has kubectl, hence my changes to the command in the CRD hook job

[fhoekstra]

And um, despite the Markdown formatting of my PR description (which looks amazing, I know) I wrote it all by hand.

This consideration is worth checking out:

There is one added maintenance burden though: the k8s registry does not keep a latest or release tag, so we'll have to keep this image tag up-to-date with recent patches.

If you are interested, I could help with configuring Renovate for this repository to keep this image tag up to date with patches automatically.

For alternatives, you could choose an image from a less trustworthy source that includes a /bin/sh and has a latest tag. This would give more convenience for you at the expense of default security posture.