add base64 PACKET_API_KEY

Fixed #95

Author: Gianluca Arbezzano

config/resources/manager/credentials.yaml

@@ -3,5 +3,5 @@ kind: Secret
 metadata:
   name: manager-api-credentials
 type: Opaque
-data:
+stringData:
   PACKET_API_KEY: ${PACKET_API_KEY}