feat: support admission.k8s.io/v1 alongside v1beta1

[mflendrich]

What this PR does / why we need it:

This PR:

• upgrades the admission.k8s.io APIs used by KIC to v1 from v1beta1. This PR assumes that a v1 webhook is backwards compatible with a v1beta1 apiserver as its caller. In other words, the webhook will accept both v1beta1 and v1 requests.
• updates ValidationWebhookConfiguration manifests to allow v1 APIs (k8s >= 1.16) alongside v1beta1.
• refactors the test for the admission controller server to table-driven for the following benefits:
  • makes it possible to introduce v1 tests alongside v1beta1 without exponential code growth
  • streamlined test execution (all tests have the same workflow but different inputs and expected outputs)
  • table-driven tests are idiomatic Go
• run each server test for v1beta1 as well as v1

Which issue this PR fixes

fixes #678

Special notes for your reviewer:
Leaves ValidationWebhookConfiguration at v1beta1 for compatibility with k8s < 1.16. Added TODOs for a later cleanup.

[hbagdi]

As discussed out of band, we need v1beta1 and v1 at the same time.

BTW, nice work with table driven test refactoring here.
Make sure to have two separate commits, one for tests refactoring and other adding the feature, helps in git spellunking in future. Thanks!

[mflendrich]

As discussed out of band, we need v1beta1 and v1 at the same time.

This PR supports both versions, according to my understanding of the admission.k8s.io documentation about (minimal) changes between these versions - v1 being essentially a promoted v1beta1 with some stricter validations. Reworded the PR description to capture it better.

BTW, nice work with table driven test refactoring here.
Make sure to have two separate commits, one for tests refactoring and other adding the feature, helps in git spellunking in future. Thanks!

Thanks! These are separate commits already.

[mflendrich]

KIC admission webhook manually verified to work with:

• kubernetes 1.15 and admission.k8s.io/v1beta1
• kubernetes 1.18 and admission.k8s.io/v1

[hbagdi]

Two minor comments but otherwise looks good.

[mflendrich]

Please take a look now @hbagdi. Added two new commits - to be autosquashed before merging.

[hbagdi]

to be autosquashed before merging.

This is not possible in Github UI, you either have squash and merge or rebase and merge. We want two commits and we will either get 1 or 4 if we do this via Github.

(Unless this is a magical Github feature that I'm missing).

[mflendrich]

done, looks like it requires another approval now 🙄

@hbagdi do we want to wait for #764 and then rebase on top of the new next?

[hbagdi]

@hbagdi do we want to wait for #764 and then rebase on top of the new next?

Sorry, I saw this comment after I merged 764 else I'd have merged this one first. Can you do a rebase please?

[mflendrich]

Can you do a rebase please?

Done.
From my perspective, the PR is ready for merging.