[Task] Handle global ARG

[taorepoara]

What should be done

Implement ARG command for global scope.

Technical recommandation

Add a global_arg field in the Dofigen struct of type HashMap<String, Option<String>>.

This may lead to patch problem...

Implement the generation of the ARG commands from the previous field.

Global scope args are not simple to implement since they can be used in fromImage and we have to define if the arg will be replaced to load image tag or just allow them in fromContext.

Is this task linked with any other ?

#250

_{Huly®: DOFIG-270}