Kustomize integration of Application Set controller and Argo CD (#87)

[jgwest]

This PR inserts new code into the generation script, to automatically render a YAML file containing

• the ApplicationSet k8s resources
• the latest stable Argo CD k8s resources (stable is latest stable release, currently '1.8.3'). This is the same URL that Argo CD references for installation in its docs, and should thus be durable.

together into a file manifests/install-with-argo-cd.yaml

I went with install-with-argo-cd.yaml as the name, if folks have a better name suggestion let me know!

To install both Argo CD and ApplicationSets, together, all one needs to do is:

kubectl install -f manifests/install-with-argo-cd.yaml

(equivalent to this section of Argo CD)

This is an alternative to the standalone Application Set install, which is kubectl install -f manifests/install.yaml

Steps for how to use this file will be added to the Installation section of the docs, as part of the existing 'user guide' issues.

Fixes #87

[wtam2018]

LGTM
Thanks @jgwest