Enhancement: Support filtering snapshots by tag and path in the stats command

We've added filtering snapshots by `--tag tagList` and by `--path path` to
the `stats` command. This includes filtering of only 'latest' snapshots or
all snapshots in a repository.

https://github.com/restic/restic/issues/2858
https://github.com/restic/restic/pull/2859
https://forum.restic.net/t/stats-for-a-host-and-filtered-snapshots/3020
