Step 1 under deploy is pointing to an incorrect Github url to all-in-one-dbless.yaml
.
Url should be https://raw.githubusercontent.com/Kong/kubernetes-ingress-controller/v2.8.1/deploy/single/all-in-one-dbless.yaml instead of https://raw.githubusercontent.com/Kong/kubernetes-ingress-controller/2.8.1/deploy/single/all-in-one-dbless.yaml