History displays a "rev" change that is incorrect

[rudimatz]

with https://github.com/ietf-tools/purple/blob/main/rpc/migrations/0010_add_rfctobe_rev.py we backfilled the "rev" value for newly added field rctobe.rev

However this save() didn't trigger a capture in history, so that now the rev change will be attributed to the next person that does a change.

e.g. https://purple.rfc-editor.org/docs/draft-nerenberg-imap-binary/history shows incorrectly that Alice set the rev, in addition to changing the "stream" which actually happened.

[rudimatz]

possible solution:

1. add migration that will create history entry for each for the "SYSTEM" user
2. cleanup the wrongly attributed changes