Conditionaly call the initContainers only when .postgresql.enable is true

[gsake]

Issue #359: Helm deploy with external database is failing due to missing Values.postgresql.image.registry

Solution: The proposed solution that is verified in my environent is to conditionaly call the initContainers only when the .postgresql.enabled is set to true and to ommit if the .postgresql.enabled is set to false

[jkiddo]

@chgl are you good with this?

[chgl]

I commented on https://github.com/hapifhir/hapi-fhir-jpaserver-starter/pull/367 - which does the same but targets the master branch which will then trigger a chart release an will run the CI