Allow custom `CacheResolver` to be configured

[snicoll]

The current CacheAutoConfiguration has the following condition: @ConditionalOnMissingBean({ CacheManager.class, CacheResolver.class }). If you want to configure your own custom CacheResolver, something along the lines of

@Bean
@Lazy
public CacheResolver fooBarCacheResolver(CacheManager cacheManager) {
    return new AbstractCacheResolver(cacheManager) { ... }
}

Then it blows up because the CacheManager is no longer configured. And it isn't because we've defined a CacheResolver.

But we haven't configured the CacheResolver: we just have configured a CacheResolver that can be used in a dedicated service.

Maybe we should use a bean name rather than a type.

The exception is also misleading:

java.lang.IllegalStateException: No CacheResolver specified, and no bean of type CacheManager found. Register a CacheManager bean or remove the @EnableCaching annotation from your configuration.