Use kustomize and envsubst to generalize k8s config.

Adds a [kustomize](https://github.com/kubernetes-sigs/kustomize) overlay
for a new staging environment. Additionally, adds environment variables
in the place of certain pieces of information that need to be templated.

The K8s README ("deploy/README.md") has been updated to reflect the new
method for applying config.

This commit also removes the configuration for the AWS cluster and
references to AWS in the README.

deploy/azure/kustomization.yaml

@@ -0,0 +1,11 @@
+namespace: atat
+resources:
+  - azure.yml
+  - atst-configmap.yml
+  - atst-envvars-configmap.yml
+  - atst-nginx-configmap.yml
+  - atst-worker-envvars-configmap.yml
+  - crls-sync.yaml
+  - pgsslrootcert.yml
+  - volume-claim.yml
+  - nginx-client-ca-bundle.yml