feat: add Flux deployment manifests for VIN Decoder service (flux/vin-decoder/)

Create flux/vin-decoder/ with namespace, HelmRelease, ExternalSecret, and
kustomization files mirroring the existing API Flux manifest structure.
Register vin-decoder in the root flux/kustomization.yaml so Flux picks it up.
Image automation is handled by existing flux/image-automation/ manifests
(ImageRepository and ImagePolicy for vin-decoder already present).

kustomize build flux/ passes with no errors.

Closes leeworks-agents/api-company#140

flux/vin-decoder/externalsecret.yaml

@@ -0,0 +1,18 @@
+apiVersion: external-secrets.io/v1beta1
+kind: ExternalSecret
+metadata:
+  name: rapidapi-proxy-secret
+  namespace: vin-decoder
+spec:
+  refreshInterval: 1h
+  secretStoreRef:
+    name: kubernetes-provider
+    kind: ClusterSecretStore
+  target:
+    name: rapidapi-proxy-secret
+    creationPolicy: Owner
+  data:
+    - secretKey: X-RapidAPI-Proxy-Secret
+      remoteRef:
+        key: rapidapi-vin-decoder-source
+        property: X-RapidAPI-Proxy-Secret