Polish "Add support for cache2k in memory caching"

See gh-28498

spring-boot-project/spring-boot-docs/src/docs/asciidoc/actuator/metrics.adoc

@@ -850,6 +850,7 @@ Additional, cache-specific metrics are also available.
 
 The following cache libraries are supported:
 
+* Cache2k
 * Caffeine
 * EhCache 2
 * Hazelcast

spring-boot-project/spring-boot-docs/src/docs/asciidoc/io/caching.adoc

@@ -44,6 +44,7 @@ If you have not defined a bean of type `CacheManager` or a `CacheResolver` named
 . <<io#io.caching.provider.couchbase,Couchbase>>
 . <<io#io.caching.provider.redis,Redis>>
 . <<io#io.caching.provider.caffeine,Caffeine>>
+. <<io#io.caching.provider.cache2k,Cache2k>>
 . <<io#io.caching.provider.simple,Simple>>
 
 Additionally, {spring-boot-for-apache-geode}[Spring Boot for Apache Geode] provides {spring-boot-for-apache-geode-docs}#geode-caching-provider[auto-configuration for using Apache Geode as a cache provider].
@@ -230,6 +231,19 @@ The auto-configuration ignores any other generic type.
 
 
 
+[[io.caching.provider.cache2k]]
+==== Cache2k
+https://cache2k.org/[Cache2k] is an in-memory cache.
+If the Cache2k spring integration is present, a `SpringCache2kCacheManager` is auto-configured.
+
+Caches can be created on startup by setting the configprop:spring.cache.cache-names[] property.
+Cache defaults can be customized using a `Cache2kBuilderCustomizer` bean.
+The following example shows a customizer that configures the capacity of the cache to 200 entries, with an expiration of 5 minutes:
+
+include::code:MyCache2kDefaultsConfiguration[]
+
+
+
 [[io.caching.provider.simple]]
 ==== Simple
 If none of the other providers can be found, a simple implementation using a `ConcurrentHashMap` as the cache store is configured.