fix: minimal kube version

Chart.yaml

@@ -1,11 +1,11 @@
-
 apiVersion: v2
 name: cmak-operator
 description: Manage and vizualize Kafka clusters with CMAK (prev. Kafka Manager).
 icon: https://www.vectorlogo.zone/logos/kubernetes/kubernetes-icon.svg
 type: application
 version: 0.0.0 # actual chart version is managed by git tags
 appVersion: 3.0.0.5-7e7a22e
+kubeVersion: ">=1.21"
 
 home: https://github.com/eshepelyuk/cmak-operator