Polish cache sample

Update single cache sample with all supported cache providers. Add README
to shortly explain how to get started with them.

See gh-2633

spring-boot-samples/spring-boot-sample-cache/src/main/resources/application.properties

@@ -0,0 +1,19 @@
+
+
+#
+# Infinispan configuration file location.
+#
+#spring.cache.infinispan.config=infinispan.xml
+
+
+#
+# JCache configuration (example with hazelcast).
+#
+#spring.cache.type=jcache
+#spring.cache.jcache.config=hazelcast.xml
+
+
+#
+# Guava configuration
+#
+#spring.cache.guava.spec=maximumSize=200,expireAfterAccess=600s