This commit introduces the necessary changes to decouple the write-ahead
logging (WAL) from the storage layer. From now on, every change
committed on the read-write node will be checkpointed immediately. The
commit will only succeed if the WAL file containing the changes has been
successfully delivered to the litelogd service. This service will then
distribute the WAL file to all read-only replicas, which will apply the
changes to their respective databases.

[Milestone 1]