Support status file for "stats" command

[brycekellogg]

According to the documentation (and my testing) the status file is not generated (or updated) when doing resticprofile stats. It looks like it only supports "backup/forget/check".

My use case is to monitor the total size of my repository via stats --mode raw-data, which the JSON output in the status file for backup doesn't seem to cover.

[creativeprojects]

Yeah I suppose that shouldn't be too difficult to implement 👍🏻