Implement additional restic functionality

[YannikBramkamp]

Make already existing functions such as ListSnapshots available via flags or commands.

[YannikBramkamp]

Current state:

Additional flags:

• --restic-check:
  Checks repository integrity with restic check. Should be useful
• --restic-prune:
  Removes any unneeded data left by for example restic forget with restic prune. Could be run after --forget
• --restic-rebuild-index:
  Rebuilds repository index with restic rebuild-index. Potentially useful, although maybe not as a flag that is run after restic backup?
• --restic-snapshots:
  List snapshots in repository with restic snapshots. Potentially useful, but maybe more in conjunction with a "blank" command?
• --restic-tags:
  Edit tags of snapshots with restic tag. Limited usefulness, especially es a flag.

In summary, as far as I can see, the first three flags would be actually useful as a flag, while --restic-tags and --restic-snapshots would be more limited in usefulness. Would it be worth considering to create a "maintenance" command that could be used to run those flags?