TarMK: Implement tooling to repair broken nodes

With oak-run check we can determine the last good revision of a repository and use it to manually roll back a corrupted segment store.

Complementary to this we should implement a tool to roll forward a broken revision to a fixed new revision. Such a tool needs to detect which items are affected by a corruption and replace these items with markers. With this the repository could brought back online and the markers could be used to identify the locations in the tree where further manual action might be needed.