Add a spring-boot-developer-tools sample

Add a sample application that demonstrates how the
`spring-boot-developer-tools` module can be used.

Closes gh-3082

spring-boot-samples/pom.xml

@@ -38,6 +38,7 @@
 		<module>spring-boot-sample-data-redis</module>
 		<module>spring-boot-sample-data-rest</module>
 		<module>spring-boot-sample-data-solr</module>
+		<module>spring-boot-sample-developer-tools</module>
 		<module>spring-boot-sample-flyway</module>
 		<module>spring-boot-sample-hateoas</module>
 		<module>spring-boot-sample-hornetq</module>