Boyscouting (#558)

* Boyscouting: Docker conventions

* Boyscouting: JUnit 5 conventions ("It is generally recommended to omit the public modifier for test classes, test methods, and lifecycle methods unless there is a technical reason for doing so)"

* Boyscouting: typo in RepositoryValidationInterceptorFactoryDstu3

* Boyscouting: use List.of instead of Guava; use StandardCharsets instead of Guava; remove unused imports

---------

Co-authored-by: Gerlach, Winfried <Winfried.Gerlach@draeger.com>

src/test/java/ca/uhn/fhir/jpa/starter/ExampleServerDstu2IT.java

@@ -21,7 +21,7 @@ import static org.junit.jupiter.api.Assertions.assertEquals;
      "hapi.fhir.fhir_version=dstu2",
      "spring.datasource.url=jdbc:h2:mem:dbr2",
   })
-public class ExampleServerDstu2IT {
+class ExampleServerDstu2IT {
 
 	private static final org.slf4j.Logger ourLog = org.slf4j.LoggerFactory.getLogger(ExampleServerDstu2IT.class);
 	private IGenericClient ourClient;