[metadata-retrieve] Export / Display package.xml based on user's selection

[tprouvot]

Is your feature request related to a problem? Please describe. It would be great to be able to select metadata details inside a metadata component. ie two or three custom labels instead of all them.

In addition to that, display the computed package.xml and a button to download it.

Describe the solution you'd like A clear and concise description of what you want to happen.

Additional context Example of workbench + Force.com migration tool