WIP: feat(commands)!: Add json output option to prune

[aawsome]

BREAKING CHANGE: Moves json to global options.

TODO:

• remove temporary dependency on branch enumset once refactor: replace dep bitmask-enum by enumset rustic_core#173 is merged into rustic_core

[simonsan]

rustic_core#173 has been merged, this needs conflicts to be resolved still. Anything else to add?

[aawsome]

rustic_core#173 has been merged, this needs conflicts to be resolved still. Anything else to add?

I think we should first thing of which information we want to display in the json output before we just serialize stats.debug. I mean, yes, it could be the information we want to present, but also something else may be wanted...

[aawsome]

Besides this, we should not mix making --json a global attribute with a json output of prune, IMO...