image-config-webpack-plugin: Add minifier for production build

[ernscht]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[ ] Performance issue
[x] Feature request
[ ] Documentation issue or request
[ ] Support request
[ ] Other... Please describe:

Current behavior

Images always stay untouched, also in production build.

Expected behavior

Images for production could be minified.

What is the motivation / use case for changing the behavior?

Lossless minificaton of images would reduce the production build size.
We coud take over the webpack config from Nitro to the image-config-webpack-plugin. It uses the img-loader with some imagemin plugins in a pre phase of the url-loader.
This config would make sense for the production build and works perfect ;-)

What do you think?