Hard-coded password for Docker Registry app

[carmat88]

Is your feature request related to a problem? Please describe. In the values.yaml file for the Docker Registry app there is an hard-coded password. While this can be okay for testing and developement, it should not be the case for a production environment.

• https://github.com/scaleoutsystems/stackn/blob/develop/apps/docker-registry/chart/values.yaml

Describe the solution you'd like Using existing secrets or creating one for the app.

How would the solution positively affect the functionality? Improving security.