config: add a config-file parser

[fionera]

There is an official one, but having one that can be used with CUE would be nice.

https://github.com/haproxytech/config-parser/

[git001]

What's CUE ?

[fionera]

What's CUE ?

CUE is a config language that supports schemas and other things
https://cuelang.org/