Consensus migration stage 1: Enable Nimbus-Aura

[Garandor]

This PR enables Nimbus-Aura consensus for Dolphin as stage 1 of #486

It creates a 3-step author filter pipeline:

1. Check that a NimbusId attached to a block seal belongs to an AccountId and is registered with
   SessionKeys
2. Check that the ValidatorId belonging to that account is part of Session::validators()
3. Select one collator from the set of eligibles per slot in round-robin fashion = aura

followup to #668
addresses #669
fixes #612

NOTE:

• Failure of docker-image-test is expected as this is a consensus-breaking change. The new client is incompatible with the currently deployed state of the calamari chain and will only work when the chain runtime is upgraded.
• Failure of dolphin- and calamari-integration-test is also expected and depends on an upstream fix in polkadot-js/api. The submitted PR is: Extend getAuthorDetails to handle Nimbus for the MantaNetwork usecase polkadot-js/api#5142

Todo:

• Enable on calamari
• runtime-benchmarks / try-runtime
• [ ] remove left-over mentions of aura
  Can't do this as we still use the Aura session key until we migrate away
• Merge service_nimbus back into service, leave old aura service used for manta as service_aura
• Upgrading manta runtime to nimbus left for a followup issue
• Localize/Fix avg block time degradation - this was a misconfiguration of local testing. block avg is 12s as normal
• Fix benchmark failure
• Fix polkadot-js API not getting block author correctly on Dolphin