Add integration tests for How-to: Implement core services with Redis

Issue gh-1019

docs/spring-authorization-server-docs.gradle

@@ -70,6 +70,7 @@ dependencies {
 	runtimeOnly "com.h2database:h2"
 	testImplementation "org.springframework.boot:spring-boot-starter-test"
 	testImplementation "org.springframework.security:spring-security-test"
+	testImplementation "com.github.codemonstur:embedded-redis:1.4.3"
 }
 
 tasks.named("test") {