"http proxy-middleware" Events Handlers don't support async methods

[marekachilles]

Checks

• I understand project setup issues should be asked on StackOverflow or in GitHub Discussions.
• I updated to latest http-proxy-middleware.

Describe the bug (be clear and concise)

The "http proxy-middleware" Events Handlers can't call on asnyc methods. It would be nice to be able to use them without a work around.

Step-by-step reproduction instructions

I use this workaround to call on async methods: 
proxyReq: (proxyReq, req, res) => {
            proxyReq.socket!.pause();
            get_user_permit(proxyReq).then((c) => {
                console.log("PERMIT ERTEILT ?", c , c!.ok());
                if(!c!.ok())
                {
                    proxyReq.destroy();
                    return;
                }         
                proxyReq.socket!.resume();         
            }).catch((err) => {
              proxyReq.socket?.destroy;
            });

Expected behavior (be clear and concise)

I should be able to call up async Methods without pausing and resuming the connection.

How is http-proxy-middleware used in your project?

Using: "http-proxy-middleware": "^3.0.0-beta.0",

What http-proxy-middleware configuration are you using?

loggerPlugin, errorResponsePlugin, proxyEventsPlugin, createProxyMiddleware, responseInterceptor

What OS/version and node/version are you seeing the problem?

Windows and node: '18.12.1'

Additional context (optional)

No response