Play 3.x / Pekko support

[PromanSEW]

Support for Play Framework 3.x and Apache Pekko
Fixes #326

[PromanSEW]

I don't know what is wrong with router in tests, I need help :(

[PromanSEW]

There are four places with links to Akka remained:
https://github.com/PromanSEW/play-socket.io/blob/play-3.x/samples/java/chat/app/chat/ChatEngine.java#L34
https://github.com/PromanSEW/play-socket.io/blob/play-3.x/samples/scala/chat/app/chat/ChatEngine.scala#L34
https://github.com/PromanSEW/play-socket.io/blob/play-3.x/docs/JavaSocketIO.md#L615
https://github.com/PromanSEW/play-socket.io/blob/play-3.x/docs/ScalaSocketIO.md#L550
What links should be here?

[mkurz]

https://github.com/PromanSEW/play-socket.io/blob/play-3.x/samples/java/chat/app/chat/ChatEngine.java#L34
https://github.com/PromanSEW/play-socket.io/blob/play-3.x/samples/scala/chat/app/chat/ChatEngine.scala#L34

https://pekko.apache.org/docs/pekko/current/stream/stream-dynamic.html

https://github.com/PromanSEW/play-socket.io/blob/play-3.x/docs/JavaSocketIO.md#L615
https://github.com/PromanSEW/play-socket.io/blob/play-3.x/docs/ScalaSocketIO.md#L550

https://pekko.apache.org/docs/pekko/current/typed/cluster.html

[PromanSEW]

Also, local testing succeed without this error in CI in Polling socket.io support tests:

play.api.PlayException: Execution exception[[UnknownSessionId: Unknown session id: 8b0acb5e-8634-4586-af70-510334c3d0d8]]