[Enhancement] use admissionregistration.k8s.io/v1

[iwilltry42]

What and why?

• admissionregistration.k8s.io/v1beta1 was deprecated in k8s v1.16
• changeset includes fetching the APIVersion and Kind from the
  admissionReviewRequest to avoid related errors

Testing Steps

Please provide adequate testing steps (including screenshots if necessary).
Include any test fixtures or sample configurations in your commit.

• existing tests pass
• deployed and verified to be working on a k8s v1.19 cluster with the following (templated) config:

apiVersion: admissionregistration.k8s.io/v1
kind: MutatingWebhookConfiguration
metadata:
  name: "tumblr-sidecar-injector-webhook"
  labels:
    app: k8s-sidecar-injector
    team: "MPOPS"
webhooks:
- name: "injector.tumblr.com"
  failurePolicy: "Ignore" # we fail "open" if the webhook is down hard
  rules:
  - operations: [ "CREATE" ]
    apiGroups: [""]
    apiVersions: ["v1"]
    resources: ["pods"]
  clientConfig:
    # https://github.com/kubernetes/kubernetes/blob/v1.10.0-beta.1/staging/src/k8s.io/api/admissionregistration/v1beta1/types.go#L218
    # note: k8s is smart enough to use 443 or the only exposed port on the service
    # note: this requires the service to serve TLS directly (not thru ingress)
    service:
      name: "k8s-sidecar-injector"
      namespace: "{{ .Release.Namespace }}"
      path: "/mutate"   # what /url/slug to send requests at
    # See README.md for how this was generated!
    caBundle: {{ required $caCertRequiredWarning (.Files.Get $caCert) | b64enc }}
  admissionReviewVersions: ["v1", "v1beta1"]
  sideEffects: None

Reviewers

Required reviewers: @byxorna
Request reviews from other people you want to review this PR in the "Reviewers" section on the right.

⚠️ this PR must have at least 2 thumbs from the MAINTAINERS.md of the project before merging!

[hemals24]

@iwilltry42 Any plans to merge this?

[iwilltry42]

@hemals24 , sure, but I'm not a maintainer, so waiting for review + merge 🤷‍♂️

[hemals24]

@byxorna The injector fails on the newer versions of k8s. This PR would fix the issue. Do you have plans to merge this?

[hemals24]

@iwilltry42 Add people as reviewers, that should help speed things up

[iwilltry42]

Unfortunately, that option is disabled and I cannot assign reviewers 🤔

[hemals24]

Strange !!! I used your code and modified it a little bit to pass the build. #60