Add Message Preprocessor in WS Adapter

[CodyTseng]

Is there an existing issue that is already proposing this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe it

The current wsAdapter only supports handling messages in the format { "event": string, "data": any }.

Describe the solution you'd like

I’ve implemented a feature in another-nestjs-ws-adapter that allows preprocessing of messages before routing. This enables the wsAdapter to handle different message formats.

Teachability, documentation, adoption, migration strategy

Add a setMessagePreprocessor method to the wsAdapter to customize how messages are preprocessed.

const wsAdapter = new WsAdapter(app);

wsAdapter.setMessagePreprocessor((message: any) => {
  const [event, ...data] = message;
  return { event, data };
});

What is the motivation / use case for changing the behavior?

I believe this would be a valuable addition to the official @nestjs/websockets package, making it more flexible for various use cases. Would it be possible to consider integrating this functionality?