Add testing directory structure and initial configuration files; introduce test-plain ConfigMap for testing purposes.

Author: max06

.cursor/rules/meta.mdc

@@ -14,6 +14,8 @@ The main entrypoint is [helmfile.yaml](mdc:helmfile.yaml). It's used for bootstr
 
 The `clusters/` directory contains a specific directory structure to define clusters or constellations (logical groups of clusters with similar tasks, deployments or just to show a common owner) with clusters.
 
+The `testing/` directory follows the exact same schema, but is only used for testing.
+
 Examples:
 
 - `clusters/in-cluster` is the upstream or management cluster. It's running rancher (for deploying and managing downstream kubernetes clusters) and argo-cd (managing all deployments on all clusters). 

apps/test-plain/configmap.yaml

@@ -0,0 +1,6 @@
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: test-plain-config
+data:
+  foo: bar

testing/cluster1/apps/uses-plain-app/config.yaml

@@ -0,0 +1 @@
+baseApp: test-plain