Devenv: create slow_proxy_mac (#19174)

devenv/docker/blocks/slow_proxy_mac/Dockerfile

+
+FROM golang:latest 
+ADD main.go /
+WORKDIR /
+RUN go build -o main . 
+EXPOSE 3011
+ENTRYPOINT ["/main"]

devenv/docker/blocks/slow_proxy_mac/docker-compose.yaml

+  slow_proxy_mac:
+    build: docker/blocks/slow_proxy_mac
+    ports:
+      - '3011:3011'
+    environment:
+      ORIGIN_SERVER: 'http://host.docker.internal:9090/'

devenv/docker/blocks/slow_proxy_mac/main.go

+package main
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+	"os"
+	"time"
+)
+
+func main() {
+	origin := os.Getenv("ORIGIN_SERVER")
+	if origin == "" {
+		origin = "http://host.docker.internal:9090/"
+	}
+
+	sleep := time.Minute
+
+	originURL, _ := url.Parse(origin)
+	proxy := httputil.NewSingleHostReverseProxy(originURL)
+
+	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		fmt.Printf("sleeping for %s then proxying request: %s", sleep.String(), r.RequestURI)
+		<-time.After(sleep)
+		proxy.ServeHTTP(w, r)
+	})
+
+	log.Fatal(http.ListenAndServe(":3011", nil))
+}