mode to ask for confirmation on writes

[jonahkagan]

create a mode that asks the user to confirm they really want to make a write before any operations that make modifications to the db. bonus points if you can show a preview of what modifications would be made

[jonahkagan]

this isn't really the responsibility of mongoose-repl. the user should either be careful or connect to a read-only secondary

[azylman]

Bonus points for present-Jonah shutting down past-Jonah.