Verification of ContainerChain AUthorship in runtime should happen during block execution

[girazoki]

Right now the runtime verification of the block seal is done with the authorities before the block was created: https://github.com/paritytech/cumulus/blob/b49628f316c1086fd2f5cc8ef2a52cceca8b8818/pallets/aura-ext/src/lib.rs#L118. While this is fine for Tanssi (otherwise runtime-APIs would suffer), we should modify this in the containerChains such that the verification happens during the block execution, and not before.
https://github.com/paritytech/substrate/blob/5380a9a513918c144175cf2a48d66a35e6e7cad4/client/consensus/aura/src/lib.rs#L511