Using Infinispan Client with Vert.x 4

[tsegismont]

We could reuse the simple counter/locks examples that @karesti contributed to the vertx-examples repo (removed in Vert.x 4 branch).

Instead of using ISPN embedded, we would explain how to use the Vert.x 4 Future/CompletableFuture to integrate the ISPN Client.

When we get a specific client for Vert.x, we can remove the interop parts.

Perhaps we could also find a way to show continuous queries (which make a perfect combo with SockJS bridge).
Or make two different how-tos?