Permit usage of notifications for metering

This patch introduces a new publisher that uses notification instead
of RPC.

And set it by default.

Closes bug: #1005933
Implements blueprint replace-rpc-cast-with-notifications
Co-Authored-By: Ala Rezmerita <ala.rezmerita@cloudwatt.com>

Change-Id: Idc40c148ef60d5e1349d30c66ba85691d93c5675
Merge "Permit usage of notifications for metering"