[EPIC] Prepare Dofigen v2

[taorepoara]

What should be done

Prepare the new Dofigen version that will include API breaking changes.

Prepare CLI API changes:

• The CLI can have subcommands in order to manage some additional tasks (ex: [Task] Generate a lock file #181)
• The ignore file is not given anymore since it is defined based on the Dockefile file ([Bug]: when using -f, generate a <dockerfile-name>.dockerignore #195)

Prepare Lib and YAML API changes:

• Use Dockerfile commands as default attribute names
• Make most of the attributes as explicit as possible by creating corresponding struct that implements FromString to be parsable as today (ex: [Task] Improve add #136)

Technical recommandation

Add many unit tests before changing anything and refactor the code to be more readable by refactoring the code using functional syntax.

• [Task] Improve unit test #199

Ecological concerns

Use more ref instead of cloning struts.

Is this task linked with any other ?

• [Bug]: Artifact copy does gives the write owner #193
• [Task] Generate a lock file #181
• [Task] Extend external definitions #180
• Add CLI unit tests #206
• Add fs binding #212
• Handle user group #215
• Use EOF in runs instead of escapes #219
• Improve cache struture #222
• Improve error display #224