Make sample to work with spring-native

- While project uses jdk8, you can do native build with jdk11
  `./mvnw clean package -Pnative`
- You can then run these
  spring-shell-samples/target/spring-shell-samples
  java -jar spring-shell-samples/target/spring-shell-samples-3.0.0-SNAPSHOT-exec.jar
- Remove logback.xml in favour of spring config to workaround for
  https://github.com/spring-projects-experimental/spring-native/issues/625
- For now remove jcommander command sample to get support for it #340
- Relates #323

spring-shell-samples/src/main/resources/application.yml

@@ -1,3 +1,3 @@
-spring:
-  main:
-    allow-circular-references: false
+logging:
+  level:
+   root: error

spring-shell-samples/src/main/resources/logback.xml

@@ -1,5 +0,0 @@
-<configuration>
-	<!-- Disable most stdout logging by default -->
-	<root level="ERROR">
-	</root>
-</configuration>