This is the implementation of the approach described here:
https://github.com/paritytech/polkadot-sdk/issues/1617#issuecomment-2150321612
&
https://github.com/paritytech/polkadot-sdk/issues/1617#issuecomment-2154357547
&
https://github.com/paritytech/polkadot-sdk/issues/1617#issuecomment-2154721395.

## Description of changes

The end goal is to have an architecture where we have single
subsystem(`approval-voting-parallel`) and multiple worker types that
would full-fill the work that currently is fulfilled by the
`approval-distribution` and `approval-voting` subsystems. The main loop
of the new subsystem would do just the distribution of work to the
workers.

The new subsystem will have:
- N approval-distribution workers: This would do the work that is
currently being done by the approval-distribution subsystem and in
addition to that will also perform the crypto-checks that an assignment
is valid and that a vote is correctly signed. Work is assigned via ...