What does this PR change? What problem does it solve?

Based on #4837 and #4838

Add a --dry-run option for the restore command. Using this option, restore will only work on metadata basis. In addition, the PR introduces a new verbose status output for the restore command. See the docs changes for an example snippet. Other possible line prefixes except restored are skipped (due to --overwrite=...) and unchanged (if the verification of existing files considers a file to be up-to-date).

• Discuss and polish restore output

Was the change previously discussed in an issue or on the forum?

restore --dry-run has been discussed in various places, including #2796 . However, no details on the log messages have been discussed.

Checklist

• I have read the contribution guidelines.
• I have enabled maintainer edits.
• I have added tests for all code changes.
• I have added documentation for relevant changes (in the manual).
• There's a new file in changelog/unreleased/ that describes the changes for our users (see template).
• I have run gofmt on the code in all commits.
• All commit messages are formatted in the same style as the other commits in the repo.
• I'm done! This pull request is ready for review.