feat: Add events for version restore

[juliusknorr]

Fixes #35511

Slightly simplified version of #26023

Since version preview is now implemented in viewer, we only need an event before a restore attempt and after success/failure.

This is needed for restoring a version while having an ongoing editing session e.g. with Collaboera as we will need to save current changes first, let Collabora handle the restore in order to have a smooth transition from the old to the restored document.

Usage can be seen in https://github.com/nextcloud/richdocuments/blob/chore/refactor-iframe/src/mixins/version.js

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)

[juliusknorr]

/backport to stable27

[skjnldsv]

Looks good!
I wonder how far we should allow ourselves to go from standard events like files:node:moved

[max-nextcloud]

/compile

[backportbot-nextcloud]

The backport to stable27 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable27
git pull origin stable27

# Create the new backport branch
git checkout -b fix/foo-stable27

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable27

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport

[juliusknorr]

/backport bb41932 to stable27