This should be reviewed commit by commit.
Nowadays it's trivial to propagate cache invalidations, which means we
can move some things off the main process, and not go through HTTP
replication.
`ReplicationGetQueryRestServlet` appeared to be unused, and was very
weird, as it was being called if the current instance is the main one…
to RPC to the main one (if no instance is set on a replication client,
it makes it to the main process)
The other two handlers could be relatively trivially moved to any
workers, moving some methods to the worker store.
**I've intentionally not removed the replication servlets yet** so that
it's safe to rollout, and will do another PR that clean those up to
remove on the N+1 version
28c9ed3ccb