Upgrade from admission/v1beta1 to admission/v1

[Sonlis]

As admissionregistration.k8s.io/v1beta1 is deprecated in kubernetes 1.16, removed in 1.22, some changes need to be done.

Changes:

• The AdmissionResponse needs more field to be set. Kind, apiVersion and response.uid are now forced to be filled, otherwise the AdmissionResponse is dismissed, which wasn't the case in admission/v1beta1. Ref: Promote admissionreview to v1 kubernetes/kubernetes#80231
• In the webhook deployment, 2 fields are added to match v1 rules.
• Import modules from GitHub instead of ambidexter repos.
• Use go.mod and go.sum, which is a newer way to manage dependencies in Go.

[AymenSegni]

As admissionregistration.k8s.io/v1beta1 is deprecated in kubernetes 1.16, removed in 1.22, some changes need to be done.

Changes:

• The AdmissionResponse needs more field to be set. Kind, apiVersion and response.uid are now forced to be filled, otherwise the AdmissionResponse is dismissed, which wasn't the case in admission/v1beta1. Ref: kubernetes/kubernetes#80231
• In the webhook deployment, 2 fields are added to match v1 rules.
• Import modules from GitHub instead of ambidexter repos.
• Use go.mod and go.sum, which is a newer way to manage dependencies in Go.

Good Job @Sonlis 👏
Thanks!