Update toolkit components

This includes a change to the components' Kustomization files to make
use of the YAML multi-doc manifests that are now attached to the GitHub
releases.

- helm-controller to v0.8.0
  https://github.com/fluxcd/helm-controller/blob/v0.8.0/CHANGELOG.md
- kustomize-controller to v0.9.0
  https://github.com/fluxcd/kustomize-controller/blob/v0.9.0/CHANGELOG.md
- source-controller to v0.9.0
  https://github.com/fluxcd/source-controller/blob/v0.9.0/CHANGELOG.md
- notification-controller to v0.9.0
  https://github.com/fluxcd/notification-controller/blob/v0.9.0/CHANGELOG.md
- image-reflector-controller to v0.7.0
  https://github.com/fluxcd/image-reflector-controller/blob/v0.7.0/CHANGELOG.md
- image-automation-controller to v0.6.0
  https://github.com/fluxcd/image-automation-controller/blob/v0.6.0/CHANGELOG.md



Signed-off-by: Hidde Beydals <hello@hidde.co>