DATABASE_URL should only be set when you enable postgres

Currently auto-deploy-image always sets application.database_url to a value (postgres test), so auto-deploy-app will set a DATABASE_URL even when you disable postgresql chart and use your own DATABASE_URL.

The solution is either:

• auto-deploy-image should only set application.database_url when you enable postgresql, and auto-deploy-app will only set DATABASE_URL if application.database_url is set
• auto-deploy-app will only set DATABASE_URL if postgresql.enabled is true.