[2.8.x] Log websocket communication problems + handle special Netty case

[mkurz]

(I am looking into this because a premium sponsor asked me because they run into problem regarding websockets.)

When a client closes a websocket connection, it's possible it sends an optional status code. Those status codes are defined here: https://www.rfc-editor.org/rfc/rfc6455#section-7.4

Now, if a client sends a status code not defined in that list (or one that is reserved for other purposes) akka-http does not care but let's the close status code pass through into the application code, so it does not distinguish between valid and invalid status codes.

Netty however is very strict, it does not pass a play.api.http.websocket.CloseMessage on into application code. As a consequence an app handling CloseMessage will never receive it, even though Netty closes the connection and actually throws an error. However, right now that error is swallowed by Play, it's impossible to see what's going on. So this pull requests adds a warning if a problem occurs. That at least gives developers a indication that something wrong happened.

Update: In the second commit of this PR i decided to not just log a warning, but to also handle the Netty close status code problem explicitly by passing the CloseMessage with the "invalid" Status code down to the app. I think this makes a lot of sense, devs should be able to react even on invalid status codes, like they can for akka-http. It's a bit tricky right now since the information is only available in the error message. However even if Netty changes that string, at least the code would fall back and log the warning, so it's at least visible somehwere:

2022-10-28 00:15:02 WARN  p.c.s.common.WebSocketFlowHandler  WebSocket communication problem: Invalid close frame getStatus code: 1201

[mkurz]

main: #11520