SCORU/Node: make the Commitment component a Worker

This is part of the goal to get concurrent components in the rollup node, included in %Functional Rollup Node (2023Q1)

A first step towards this is encapsulating the publishing and cementing of commitments into a new worker. Some parts of the Components.Commitment module (namely creating and storing new commitments) shouldn't be part of this worker, as it belongs to the Daemon's main loop.