refactor(policy): implement builder pattern for EndPoint

src/policy/src/main/java/eu/teraflow/policy/Serializer.java

.../main/java/eu/teraflow/policy/context/model/EndPoint.java

...rc/test/java/eu/teraflow/policy/EndPointCreationTest.java

...licy/src/test/java/eu/teraflow/policy/SerializerTest.java

src/policy/target/kubernetes/kubernetes.yml