chore: set PULL_SECRET_NAME env when using a pull secret (cloudnative-pg#2019)

Signed-off-by: Marco Nenciarini <marco.nenciarini@enterprisedb.com>

Author: mnencia

config/default/manager_image_pull_secret.yaml

@@ -9,5 +9,8 @@ spec:
     spec:
       containers:
       - name: manager
+        env:
+        - name: PULL_SECRET_NAME
+          value: cnpg-pull-secret
       imagePullSecrets:
       - name: cnpg-pull-secret