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

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

I agree with Gunnar

> I simply suspect that it's always going to be great, but this can't be tested by the Infinispan team until we have a release providing the option.

So humor me here. If it is always great, why is the default not true? And why does it even need to be an option? Should it not be set out of the box? I also find it questionable to add this option into a final release exposing it to users without testing it. Why can the Infinispan team not build and test against a snapshot build containing this change verifying there is a true beneficial effect. I find the approach of adding an option, because it might help questionable.