Improve kustomization usage

Ensure that the `manifest/base` folder can be used as a standalone
kustomization resource.

Add a new subfolder `manifest/gpu` which uses `manifest/base` with
additional GPU related patches.

kubernetes/manifest/base/kustomization.yaml

@@ -0,0 +1,8 @@
+resources:
+  - open-webui.yaml
+  - ollama-service.yaml
+  - ollama-statefulset.yaml
+  - webui-deployment.yaml
+  - webui-service.yaml
+  - webui-ingress.yaml
+  - webui-pvc.yaml