Unwrap CompletionException in GrpcClient

GrpcClient expects Exceptions of a specific type but as it is right now it will not handle any exceptions as they are propagated as CompletionException
This will not solve any similar issues for any other class using ClientTelemetry, and a better solution would probably be to never wrap the exception, however that would require more intrusive changes to the future chain.
Fixes #287

Author: marcuslyth

db-client-java/src/main/java/com/eventstore/dbclient/GrpcClient.java

@@ -9,6 +9,7 @@
 import java.util.Optional;
 import java.util.UUID;
 import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Function;
@@ -79,6 +80,10 @@ public <A> CompletableFuture<A> runWithArgs(Function<WorkItemArgs, CompletableFu
                 }
 
                 try {
+                    if (error instanceof CompletionException) {
+                        error = error.getCause();
+                    }
+
                     if (error instanceof NotLeaderException) {
                         NotLeaderException ex = (NotLeaderException) error;
                         // TODO - Currently we don't retry on not leader exception but we might consider