Add Couchbase cache support

This commit updates the cache auto-configuration to provide a
`CouchbaseCacheManager` if a `Bucket` has been configured.

The global customizer infrastructure allows to further tune the cache
manager if necessary.

Closes gh-5176

spring-boot-samples/spring-boot-sample-cache/README.adoc

@@ -7,6 +7,7 @@ abstraction is supported by many caching libraries, including:
 * `EhCache`
 * `Hazelcast`
 * `Infinispan`
+* `Couchbase`
 * `Redis`
 * `Guava`
 * Simple provider based on `ConcurrentHashMap`
@@ -78,6 +79,12 @@ can set the `spring.cache.infinispan.config` property to use the provided
 
 
 
+=== Couchbase
+Add the `java-client` and `couchbase-spring-cache` dependencies and make sure that you
+have setup at least a `spring.couchbase.bootstrap-hosts` property.
+
+
+
 === Redis
 Add the `spring-boot-starter-data-redis` and make sure it is configured properly (by default,
 a redis instance with the default settings is expected on your local box).

spring-boot-samples/spring-boot-sample-cache/pom.xml

@@ -69,6 +69,16 @@
 		</dependency>
 		-->
 		<!--
+		<dependency>
+			<groupId>com.couchbase.client</groupId>
+			<artifactId>java-client</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>com.couchbase.client</groupId>
+			<artifactId>couchbase-spring-cache</artifactId>
+		</dependency>
+		-->
+		<!--
 		<dependency>
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-data-redis</artifactId>