feat: add service registration & service discovery & load balancing

[li-jin-gou]

What type of PR is this?

feat

What this PR does / why we need it (English/Chinese):

• en: add service registration & service discovery & load balancing
• ch: 添加服务注册注册 & 服务发现 & 负载均衡

Which issue(s) this PR fixes:

example:

https://github.com/li-jin-gou/nacos-demo/tree/main/example

• server

                addr := "127.0.0.1:8889"
		r := nacos_demo.NewNacosRegistry(cli)
		h := server.Default(
			server.WithHostPorts(addr),
			server.WithRegistry(r, &registry.Info{
				ServiceName: "hertz.test.demo",
				Addr:        utils.NewNetAddr("tcp", addr),
				Weight:      10,
				Tags:        nil,
			}))
		h.GET("/ping", func(c context.Context, ctx *app.RequestContext) {
			ctx.JSON(consts.StatusOK, utils.H{"ping": "pong2"})
		})
		h.Spin()

• client:

	r := nacos_demo.NewNacosResolver(naocsCli)
	cli.Use(sd.Discovery(r))
	for i := 0; i < 10; i++ {
		status, body, err := cli.Get(context.Background(), nil, "http://hertz.test.demo/ping", config.WithSD(true))
		if err != nil {
			hlog.Fatal(err)
		}
		hlog.Infof("code=%d,body=%s", status, string(body))
	}

2022/07/26 13:52:47.310617 main.go:46: [Info] code =200, body ={"ping":"pong2"}
2022/07/26 13:52:47.311019 main.go:46: [Info] code = 200, body ={"ping":"pong1"}
2022/07/26 13:52:47.311186 main.go:46: [Info] code = 200, body ={"ping":"pong1"}
2022/07/26 13:52:47.311318 main.go:46: [Info] code = 200, body ={"ping":"pong1"}
2022/07/26 13:52:47.311445 main.go:46: [Info] code = 200, body ={"ping":"pong1"}
2022/07/26 13:52:47.311585 main.go:46: [Info] code = 200, body ={"ping":"pong2"}
2022/07/26 13:52:47.311728 main.go:46: [Info] code = 200, body ={"ping":"pong1"}
2022/07/26 13:52:47.311858 main.go:46: [Info] code = 200, body ={"ping":"pong1"}
2022/07/26 13:52:47.311977 main.go:46: [Info] code = 200, body ={"ping":"pong1"}
2022/07/26 13:52:47.312107 main.go:46: [Info] code = 200, body ={"ping":"pong1"}

[welkeyever]

lgtm