Add a RESTIC_PROGRESS_FPS environment variable to limit the interval
at which the progress indicator updates (allowed values: 1-60).
The default rate of 60 FPS can cause high terminal CPU load on some
systems, like iTerm2 on macOS with font anti-aliasing enabled.
Usage:
RESTIC_PROGRESS_FPS=1 restic ...
RESTIC_PROGRESS_FPS=60 restic ...