Plumbing to increase pvf workers configuration based on chain id (#4252)

Part of https://github.com/paritytech/polkadot-sdk/issues/4126 we want
to safely increase the execute_workers_max_num gradually from chain to
chain and assess if there are any negative impacts.

This PR performs the necessary plumbing to be able to increase it based
on the chain id, it increase the number of execution workers from 2 to 4
on test network but lives kusama and polkadot unchanged until we gather
more data.

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Signed-off-by: Alexandru Gheorghe <alexandru.gheorghe@parity.io>