add USER to dockerfile

[rbaumgar]

By adding USER (e.g. USER 100) to the dockerfile. image will not run as root.

If needed, add

RUN chgrp -R 0 /some/directory \
  && chmod -R g+rwX /some/directory 

This is the message you get, when deploying on OpenShift (helm install ...)
would violate PodSecurity "restricted:latest": allowPrivilegeEscalation != false (container "dynu-webhook" must set securityContext.allowPrivilegeEscalation=false), unrestricted capabilities (container "dynu-webhook" must set securityContext.capabilities.drop=["ALL"]), runAsNonRoot != true (pod or container "dynu-webhook" must set securityContext.runAsNonRoot=true), seccompProfile (pod or container "dynu-webhook" must set securityContext.seccompProfile.type to "RuntimeDefault" or "Localhost")

Install/Deployment works fine.