For the next upcoming "major" release of Keptn

Starting with 1.19, Kubernetes changed its implementation of networking, e.g.
apiVersion: networking.k8s.io/v1beta1 became apiVersion: networking.k8s.io/v1. This is a breaking change announced for 1.22 (due in August 2021) - see Deprecation Guide for 1.22

We painfully realized that those two versions are incompatible (see PR keptn/examples#180 ), which requires us to maintain both for our docs and tutorials.

As Kubernetes 1.19 is already available at GKE (checked on June 18th, 2021), I recommend that we can raise the minimum required Kubernetes version from 1.14 to 1.19 for the upcoming release.

Definition of Done

• Every occurrance of networking.k8s.io/v1beta1 has been changed to networking.k8s.io/v1 (cli, examples, tutorials) and the manifests have been adapted accordingly
• Minimum required Kubernetes version set to 1.19 in CLI and CI Jobs
• Maximum supported Kubernetes version set to 1.22 in CLI and CI Jobs
• Keptn manually tested for AKS 1.19 and EKS 1.19
• Integration Tests: Keptn automatically tested on Kubernetes 1.19 and 1.22 (e.g. using K3s)
• Docs https://keptn.sh/docs/0.8.x/operate/k8s_support/ (replace 0.8.x with 0.9.x if available) updated