Refactor release workflow

[stefanprodan]

Changes:

• switch to ncipollo/release-action as GitHub has abandoned Mark this repository as unmaintained actions/create-release#119 and Mark this repository as unmaintained actions/upload-release-asset#78
• add notification-controller CRDs and Deployment manifests to GitHub releases assets, this will allow us to use them as remote bases in flux2 instead of extracting them from the zip asset, ref: kustomize v4 high-impact breaking changes flux2#918

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - https://github.com/fluxcd/notification-controller/releases/download/v0.9.0/notification-controller.crds.yaml
  - https://github.com/fluxcd/notification-controller/releases/download/v0.9.0/notification-controller.deployment.yaml

• drop the notification-controller.yaml asset, people can build their own with:

kustomize build https://github.com/fluxcd/notification-controller/config/default?ref=v0.8.1