`polkadot-parachain`: add manual seal support #3996

Job	Run time
preflight / preflight	40s
build (polkadot-availability-recovery, availability-recovery-regression-bench)	8m 48s
build (polkadot-availability-distribution, availability-distribution-regression-bench)	6m 40s
build (polkadot-node-core-approval-voting, approval-voting-regression-bench)	27m 50s
build (polkadot-statement-distribution, statement-distribution-regression-bench)	5m 31s
publish-benchmarks	0s
	49m 29s

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