Progress bar on non-interactive runs

[Ekleog]

When running in a systemd service, rustic gives zero indication of progress. For long backups (eg. hours-long), this can be pretty destabilizing.

Suggested change:

This command currently displays nothing until the backup completes:

$ rustic backup /home --json --progress-interval 1s &| cat

Instead, setting progress-interval would have rustic output one line per second, with a quick summary of what otherwise would be written in the progress bar. It might also make sense to have a non-interactive progress-interval defaulting to like 10 seconds.

What do you think about it?

Anyway, I'm in the process of migrating from borgmatic to rustic after borgmatic started freezing on me with week-long backups, and it looks much more usable than borgmatic for now, and easier to understand. So thank you for all the work you're putting in here!