move reflog into database

[aryairani]

and prompt to delete file that is in everyone’s home dir, whoops

[aryairani]

Instead of a prompt and deletion, we can just put it into the release notes.

[ChrisPenner]

https://unisonlanguage.slack.com/archives/C03MY5TMKT6/p1661376576351379

Had some conversation in the public slack; the rough plan is:

• Undo tree and reflog are separate things
• Reflog is a linear list of (timestamp, root-namespace-hash)
  • This reflog can be used for codebase history/push metrics on share.
• Undo tree is a tree of (undoID, timestamp, root-namespace-hash, parentUndoID)
  • This allows undo/redo, and also allows deeper analysis if desired

[aryairani]

#3364 implements the local/ucm move into the database ~~this ticket can be repurposed for the share version~~