HSEARCH-1728 introduce new `metadata_writes_async` configuration property for Infinispan

 - https://hibernate.atlassian.net/browse/HSEARCH-1728

Ok, you surely know what you are doing.

Just coming from a user perspective I can say that I really dislike this sort of option, not really documented, unclear when to set it. What does it do, in which situation should I set it? Personally I think options of this kind add up to the perceived complexity of a library and make people not want to use it because its a thing with too many knobs.