+tes #16431 support for TestProbe with user-defined name

TestProbe can be given a user-defined name

```scala
val worker1 = TestProbe("worker1")
val worker2 = TestProbe("worker2")
```
how about a more specific check:

```scala
worker.ref.name should startWith ("worker")
```

shows a bit nicer what to expect from the name IMO, same on Java example