Bugfix/resources usage

bugfix:

• handling of java min and max heap size via env variables for tomcat startup
• implemented min required default values if nothing defined in env
• includes usage examples in docker-compose files

successfully tested: https://jenkins.daasi.int/view/Modular-Build-Services/job/IDP/job/daasi-idp_docker_build_and_deploy/17/ and deployed on docker3.daasi.de (https://idp2.daasi.de/idp/status)