Nimbus Consensus Migration Stage 1

[Garandor]

This is stage 1 of the phased Nimbus consensus rollout described in #486

We aim to enable the nimbus-aura consensus mechanism on dolphin

It will consist of 2 distinct runtime upgrades implemented in succession:

• Switch to nimbus
  • Merge code that will enable nimbus-aura & disable cumulus-aura Consensus migration stage 1: Enable Nimbus-Aura #582
  • Merge code that will enable to new client to sync from genesis and verify Aura blocks correctly Support verification of historic Aura blocks #763
  • client upgrade 2 manta-run nodes
  • runtime upgrade
  • Upgrade the rest of the nodes
• Removal of Aura pallets, keys, storage #740
  • Merge a migration that will call upgrade_keys to remove aura keys
  • optional: add/enable parachain-staking ( this would merge stage 2 into this )
  • runtime_upgrade

Tests:

• Deploy 3.2.1 testnet, runtime upgrade to 3.3.0
• Add collator
• Remove collator