feat(commands): Add lock command

[aawsome]

This PR adds new commands to lock (parts of) the repository:

• lock repository to lock the complete repository. This can invalidate update/remove operations; it is suggested to use feat: Add append-only repository mode rustic_core#164 to mark the repository append-only before doing this!
• lock keys to lock all keys. This can invalidate key removal.
• lock snapshots to lock snapshots and needed pack files. This also sets an mark to the snapshots/pack files such that

see #1050

depends on rustic-rs/rustic_core#163

Also fixes the handling of delete-protected snapshots in the forget command when snapshots are explicitly given

TODO:

• remove temporary Cargo.toml change once the above PR is merged into rustic_core
• Maybe add more options to specify the "until when" timestamp. e.g. a alternative --until option.
• Think about whether we want to require to have append-only mode for lock repository.
• Think about a similar mechanism only for keys to lock
• Maybe add possibility to only lock given keys