Add support for streaming event data for DB changes

[oubiwann]

This can be done via Logical Decoding Output plugins in Postgres and some WAL/replication configuration setup.

Tasks:

• Explore the basic features and possibilities
• Install wal2json and experiment with it (see Install epgl and experiment with streaming changes #41)
• Install epgl and experiment with it (see Install epgl and experiment with streaming changes #41)
• Decide upon a plugin
• Create a new server in the mush supervision tree that manages event data (see Manage event data stream from DB #42)