Make AbstractCouchbaseConfiguration.authenticator an @Bean

[mikereiche]

Make AbstractCouchbaseConfiguration.authenticator an @bean so that CouchbaseAutoConfiguration.couchbaseAuthenticator() does not get used instead. Also make consuming authenticator() in AbstractCouchbaseConfiguration a parameter so it gets the @bean.

https://github.com/spring-projects/spring-boot/blob/03787364be2ae4ed8d1d10526ea8f6b32cd9765a/module/spring-boot-couchbase/src/main/java/org/springframework/boot/couchbase/autoconfigure/CouchbaseAutoConfiguration.java#L114