New helper function `FindFilteredSnapshots` to iterate over snapshots
New helper function `FindFilteredSnapshots` to iterate over snapshots

This helper function takes a set of filters and/or a list of snapshots
from the commandline. It returns a channel of *Snapshot.

When snapshot ids are given, they are checked for validity and their
corresponding Snapshots returned. The snapshot id "latest" is handled
special to return either the last snapshot (no filters) or the last
snapshot matching the filters.

When no arguments are given, the filters are applied over all available
snapshots and these are returned.

byo/restic,byo/restic,restic/restic,fawick/restic,jayme-github/restic,stuertz/restic,ar-jan/restic,kurin/restic,restic/restic,ar-jan/restic,middelink/restic,middelink/restic,jayme-github/restic,kurin/restic,stuertz/restic,fawick/restic