feat: #be sketch k8s dev/stg envs

backend/kustomize/kustomization.yaml

backend/kustomize/overlays/dev/database.deployment.yaml

backend/kustomize/overlays/dev/kustomization.yaml

backend/kustomize/overlays/dev/webserver.deployment.yaml

backend/kustomize/overlays/staging/deployment.yaml

backend/kustomize/overlays/staging/ingress.yaml

backend/kustomize/overlays/staging/kustomization.yaml

backend/kustomize/overlays/stg/database.deployment.yaml

backend/kustomize/overlays/stg/kustomization.yaml

backend/kustomize/overlays/stg/webserver.deployment.yaml