cleanup HTTP proxy session when device disconnects

Previously, when a device disconnected, the associated HTTP proxy session
remained in the httpProxySessions store, causing a memory leak. This commit
adds a goroutine that monitors the context cancellation and automatically
deletes the session from the store when ctx.Done() is triggered.

This ensures proper cleanup of proxy sessions when devices disconnect,
preventing resource accumulation over time.

Signed-off-by: Jianhui Zhao <zhaojh329@gmail.com>

http.go

@@ -340,6 +340,11 @@ func httpProxyRedirect(a *APIServer, c *gin.Context, group string) {
 	ses.Expire()
 	httpProxySessions.Store(sid, ses)
 
+	go func() {
+		<-ctx.Done()
+		httpProxySessions.Delete(sid)
+	}()
+
 	log.Debug().Msgf(`new httpProxySession "%s" for device "%s"`, sid, devid)
 
 	domain := c.Request.Header.Get("HttpProxyRedirDomain")