fix(maintenance): Show a success message on data-fingerprint command

[nickvergessen]

Summary

1. Enable maintenance mode
2. (optional: restore a backup)
3. Run occ maintenance:data-fingerprint
4. Be unsure if the command worked as you only read something about maintenance mode.
5. Wonder if you need to allow clients to sync again before being able updating the fingerprint

Before	After

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[nickvergessen]

/backport to stable30

[nickvergessen]

/backport to stable29

[nickvergessen]

/backport to stable28