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/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>