refactor: rename k8s-manifests directory to manifests

- Rename all `k8s-manifests` subdirectories and files to `manifests`
- Update all file paths in `argocd-init.yml` to reflect the new directory name

🤖

manifests/ingress-nginx.jsonnet

@@ -0,0 +1,30 @@
+local app = import "../_templates/argocd_app.libsonnet";
+
+[
+app + {
+  chart:: "ingress-nginx",
+  repo:: "https://kubernetes.github.io/ingress-nginx",
+  version:: "4.7.*",
+  values:: |||
+    defaultBackend:
+      enabled: true
+      image:
+        registry: ghcr.io
+        image: tarampampam/error-pages
+        tag: 2.13.0
+    controller:
+      watchIngressWithoutClass: true
+      custom-http-errors: "400,401,403,404,405,407,408,409,410,411,412,413,416,418,429,500,502,503,504,505"
+      image:
+        pullPolicy: Always
+      service:
+        externalTrafficPolicy: Local
+      metrics:
+        enabled: true
+        serviceMonitor:
+          enabled: true
+          additionalLabels:
+            release: prometheus-grafana  # same as prometheus-community chart name
+  |||
+}
+]