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/cert-manager/letsencrypt-issuers.yml

@@ -0,0 +1,34 @@
+---
+apiVersion: cert-manager.io/v1
+kind: ClusterIssuer
+metadata:
+  name: letsencrypt-prod
+  namespace: cert-manager
+  annotations:
+    argocd.argoproj.io/sync-options: SkipDryRunOnMissingResource=true
+spec:
+  acme:
+    server: https://acme-v02.api.letsencrypt.org/directory
+    privateKeySecretRef:
+      name: le-prod-account-key
+    solvers:
+      - http01:
+          ingress:
+            class: nginx
+---
+apiVersion: cert-manager.io/v1
+kind: ClusterIssuer
+metadata:
+  name: letsencrypt-staging
+  namespace: cert-manager
+  annotations:
+    argocd.argoproj.io/sync-options: SkipDryRunOnMissingResource=true
+spec:
+  acme:
+    server: https://acme-staging-v02.api.letsencrypt.org/directory
+    privateKeySecretRef:
+      name: le-staging-account-key
+    solvers:
+      - http01:
+          ingress:
+            class: nginx