Add and use golang user

Dockerfile

@@ -0,0 +1,8 @@
+FROM golang:alpine
+
+WORKDIR /app
+
+RUN adduser --disabled-password golang \
+  && chown golang:golang -R /app
+
+USER golang

docker-compose.yaml

@@ -1,6 +1,6 @@
 services:
   app:
-    image: "golang:alpine"
+    build: "."
     volumes:
       - "./:/app"
     working_dir: /app