feat!: Add more locking possibilities

[aawsome]

based on #163

see https://github.com/rustic-rs/rustic/discussions/1050

BREAKING CHANGES:

• DeleteOptions in SnapshotFile now has more enum options.
• Repository::save_snapshots now returns the list of Ids of the saved snapshots.
• RepoId now must also impl Debug

Missing points:

• [ ] Handle duplicate snapshots correctly - especially create at max. 1 new snapshot per "original" snapshot during lock
• [ ] Handle locks in forget command (retention policy: only count one/the original snapshot for retention)
• [ ] Handle locks correctly in the tag command (don't even try to remove locked snapshots)