refactor(Dockerfile): optimize container image

[Hazmi35]

Some points:

• We don't need label on build stage, you don't label incomplete products in factory yes?
• It is prefered to use --no-cache in apk, to not cache package indexes, especially in final image, and will reduce image size
• Golang is a compiled language, without any Intermediate Language like Bytecode in Java, thus you don't need to install Golang in final image
• It is advised to not run your app as a PID 1 in container, and using an init system. For containers, we just need a simple init system like tini, some of the benefits you can see here: why-tini

This reduces image from 320MB to 71.4MB in size.