feat: implement example-go service with Docker support

- Add a new Makefile with build, docker-build, test, and clean targets, including cross-compilation support for Linux AMD64 and ARM64.
- Introduce a new Go executable `example-go` with a basic HTTP server setup.
- Create a new Dockerfile for an Alpine-based container including the `example-go` binary, with metadata labels and an entrypoint.

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

cmd/example-go/main.go

@@ -0,0 +1,13 @@
+package main
+
+import (
+	"gitea.com/action-examples/go/router"
+)
+
+func main() {
+	r := router.New()
+	// listen and serve on 0.0.0.0:8080 (for windows "localhost:8080")
+	if err := r.Run(); err != nil {
+		panic(err)
+	}
+}