LiteScale previously established a new remote procedure call (RPC) each time it
needed to exchange messages among its peers. This method introduced significant
overhead because every message required a fresh negotiation for the RPC, leading
to inefficiencies in performance and resource usage.

This commit addresses these inefficiencies by implementing gRPC streams for peer
messaging. Using gRPC streams allows connections to remain open between peers,
eliminating the need for repeated RPC negotiations. As a result, we reduce
unnecessary overhead and improve the overall performance of message exchanges,
making the system more efficient and scalable.

[Milestone 2]

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]