Support loading custom profiles for validation

[chgl]

If I understand https://ibm.github.io/FHIR/guides/FHIRValidationGuide correctly, in order to validate against custom profiles (e.g. in NPM format), one first has to build a .jar and copy it "into the IBM FHIR server’s userlib directory to make it available to the server during startup."

This could be supported in (at least) two ways:

1. build a custom image already containing the .jar in the userlib dir
2. use an init/sidecar container to load the .jar from an external source (http, git, s3) and mount it inside a volume shared with the main server container (this is similar to what the airflow chart uses to fetch scripts to execute: https://github.com/bitnami/charts/tree/master/bitnami/airflow#option-2-get-your-dag-files-from-a-git-repository)

[chgl]

I just noticed #34 where I even commented the exact same thing...