feat: migrate elastic-system to ArgoCD (#79)

Migrate ECK operator from Terragrunt to ArgoCD/Kustomize.
Deploys eck-operator v3.2.0 with 2 replicas and PodDisruptionBudget
in the elastic-system namespace.

💘 Generated with Crush

Assisted-by: Claude Sonnet 4.6 via Crush <crush@charm.land>

Reviewed-on: #79

apps/base/elastic-system/kustomization.yaml

@@ -0,0 +1,6 @@
+---
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+resources:
+  - namespace.yaml

apps/base/elastic-system/namespace.yaml

@@ -0,0 +1,7 @@
+---
+apiVersion: v1
+kind: Namespace
+metadata:
+  labels:
+    app.kubernetes.io/name: elastic-system
+  name: elastic-system