Add a journal replayer for the revision layer
This simple replayer implementation is probably not good enought for a
real life scenario; especially since it will probably not be robust
enought against out-of-order kafka messages handling.
Should be ok now (maybe).
As usual when kafka is involved in tests, provided new tests are a bit slow...
Depends on !153 (closed) Related to #4616 (closed)
Migrated from D8658 (view on Phabricator)