feat: deploy argocd-image-updater via Helm

Deploys ArgoCD Image Updater into the argocd-image-updater namespace.
Vault-managed secrets provide registry credentials for git.unkin.net
and an ArgoCD API token.

Prerequisites before syncing:
- Create Vault role argocd-image-updater in k8s/au/syd1
- Populate kv/service/argocd-image-updater/registry-creds (key: creds, value: <user>:<token>)
- Create ArgoCD local user image-updater and store token at kv/service/argocd-image-updater/argocd-token

apps/overlays/au-syd1/argocd-image-updater/kustomization.yaml

@@ -0,0 +1,14 @@
+---
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+resources:
+  - ../../../base/argocd-image-updater
+
+helmCharts:
+  - name: argocd-image-updater
+    repo: https://artifactapi.k8s.syd1.au.unkin.net/api/v1/virtual/helm
+    version: "0.10.3"
+    releaseName: argocd-image-updater
+    namespace: argocd-image-updater
+    valuesFile: values.yaml

apps/overlays/au-syd1/argocd-image-updater/values.yaml

@@ -0,0 +1,33 @@
+config:
+  argocd:
+    grpcWeb: false
+    serverAddress: argocd-server.argocd
+    insecure: true
+    plaintext: false
+
+  registries:
+    - name: git.unkin.net
+      api_url: https://git.unkin.net
+      prefix: git.unkin.net
+      credentials: secret:argocd-image-updater/registry-creds#creds
+      insecure: false
+
+authScripts:
+  enabled: false
+
+extraEnv:
+  - name: ARGOCD_TOKEN
+    valueFrom:
+      secretKeyRef:
+        name: argocd-token
+        key: token
+
+gitCommitUser: "ArgoCD Image Updater"
+gitCommitEmail: "argocd-image-updater@unkin.net"
+
+rbac:
+  enabled: true
+
+serviceAccount:
+  create: true
+  name: argocd-image-updater