Nacos 2.0.0 Subscriber app is fixed at unknown

[Jisfeng]

Describe the bug
Version：Nacos 2.0.0
当客户端指定project.name属性后，订阅服务时，Nacos控制台订阅列表中应用名仍然显示unknown

Expected behavior
应该显示客户端指定的app

原因：在SubscribeServiceRequestHandler#handle中，创建Subscriber对象时写死了app=unknown

        Subscriber subscriber = new Subscriber(meta.getClientIp(), meta.getClientVersion(), "unknown",
                meta.getClientIp(), namespaceId, groupedServiceName, 0, request.getClusters());

解决办法参考：客户端会在request的header里添加了app，服务端可以从request的header中获取

        String app = request.getHeader("app", "unknown");
        Subscriber subscriber = new Subscriber(meta.getClientIp(), meta.getClientVersion(), app,
                meta.getClientIp(), namespaceId, groupedServiceName, 0, request.getClusters());

[horizonzy]

hello，你能提一个pr来修复吗。

[realJackSun]

I think this problem has been solved.