fix: avoid setting configmap name with config.secret=true

[phisco]

Fixes #156

with config.secret=false:

$ helm template test --set config.secret=false charts/cloudnative-pg | grep cnpg-controller-manager-config -C 5
# limitations under the License.
#
apiVersion: v1
kind: ConfigMap
metadata:
  name: cnpg-controller-manager-config
  labels:
    helm.sh/chart: cloudnative-pg-0.19.0
    app.kubernetes.io/name: cloudnative-pg
    app.kubernetes.io/instance: test
    app.kubernetes.io/version: "1.21.0"
--
    spec:
      containers:
      - args:
        - controller
        - --leader-elect
        - --config-map-name=cnpg-controller-manager-config
        - --webhook-port=9443
        command:
        - /manager
        env:
        - name: OPERATOR_IMAGE_NAME

with config.secret=true:

$ helm template test --set config.secret=true charts/cloudnative-pg | grep cnpg-controller-manager-config -C 5
#
apiVersion: v1
kind: Secret
type: Opaque
metadata:
  name: cnpg-controller-manager-config
  labels:
    helm.sh/chart: cloudnative-pg-0.19.0
    app.kubernetes.io/name: cloudnative-pg
    app.kubernetes.io/instance: test
    app.kubernetes.io/version: "1.21.0"
--
    spec:
      containers:
      - args:
        - controller
        - --leader-elect
        - --secret-name=cnpg-controller-manager-config
        - --webhook-port=9443
        command:
        - /manager
        env:
        - name: OPERATOR_IMAGE_NAME