feat: add pre-commit configuration (#9)

- add pre-commit-config
- add yamllint config
- add ci/validate-* custom scripts
  - verify no secrets added
  - verify clusters with kustomize and kubeconform
  - verify apps with kustomize and kubeconform

Reviewed-on: #9

ci/validate-apps.sh

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+KUBE_VERSION="1.33.7"
+
+schema_args=(
+  -schema-location "https://raw.githubusercontent.com/yannh/kubernetes-json-schema/master/{{.NormalizedKubernetesVersion}}-standalone{{.StrictSuffix}}/{{.ResourceKind}}{{.KindSuffix}}.json"
+  -schema-location "https://raw.githubusercontent.com/datreeio/CRDs-catalog/main/{{.Group}}/{{.ResourceKind}}_{{.ResourceAPIVersion}}.json"
+)
+
+while IFS= read -r -d "" k; do
+  dir="$(dirname "$k")"
+  echo "==> kubeconform: $dir" >&2
+
+  kustomize build --enable-helm "$dir" \
+    | kubeconform \
+        -kubernetes-version "$KUBE_VERSION" \
+        -summary \
+        -output pretty \
+        -verbose \
+        -skip CustomResourceDefinition \
+        "${schema_args[@]}"
+done < <(find apps/overlays -name kustomization.yaml -print0)