First cut to spawner

Co-authored-by: Roberto Abdelkader Martínez Pérez <robertomartinezp@gmail.com>

internal/server/user/spawn.go

@@ -0,0 +1,22 @@
+package user
+
+import (
+	"io"
+	"os"
+	"os/exec"
+
+	"github.com/BBVA/kapow/internal/server/model"
+)
+
+func spawn(h *model.Handler, out io.Writer) error {
+	cmd := exec.Command(h.Route.Entrypoint)
+	if out != nil {
+		cmd.Stdout = out
+	}
+	cmd.Env = append(os.Environ(), "KAPOW_URL=http://localhost:8081")
+	cmd.Env = append(cmd.Env, "KAPOW_HANDLER_ID="+h.ID)
+
+	err := cmd.Run()
+
+	return err
+}