feat: migrate cert-manager from Terraform to ArgoCD (#42)

- Add cert-manager base ArgoCD application with namespace, RBAC resources
- Create cert-manager overlay for au-syd1 with Helm chart configuration
- Update platform ApplicationSet to include cert-manager deployment
- Configure cert-manager v1.19.2 with jetstack Helm repository
- Maintain one-to-one migration from Terraform configuration

Reviewed-on: #42

apps/overlays/au-syd1/cert-manager/kustomization.yaml

@@ -0,0 +1,14 @@
+---
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+resources:
+  - ../../../base/cert-manager
+
+helmCharts:
+  - name: cert-manager
+    repo: https://charts.jetstack.io
+    version: "v1.19.2"
+    releaseName: cert-manager
+    namespace: cert-manager
+    valuesFile: values.yaml

apps/overlays/au-syd1/cert-manager/values.yaml

@@ -0,0 +1,29 @@
+crds:
+  enabled: true
+
+replicaCount: 2
+
+resources:
+  requests:
+    cpu: 10m
+    memory: 32Mi
+
+strategy:
+  type: RollingUpdate
+  rollingUpdate:
+    maxSurge: 0
+    maxUnavailable: 1
+
+webhook:
+  replicaCount: 2
+  resources:
+    requests:
+      cpu: 10m
+      memory: 32Mi
+
+cainjector:
+  replicaCount: 2
+  resources:
+    requests:
+      cpu: 10m
+      memory: 32Mi