apex-pdp dockerfile is not consistent with other policy framework dockerfiles, notably it uses a user called 'apexuser' instead of 'policy' user.
This task is to change the dockerfile to use 'policy' user, as defined in the policy-jre-alpine base image. Care must be taken as 'apexuser' is referenced in various shell scripts.

Additionally, the dockerfile uses the policy-jdk-alpine base image instead of policy-jre-alpine (policy-jdk image includes JDK, maven, python, pip, etc., none of which are needed for apex-pdp at runtime).