elastic scaling: add core selector to cumulus (#5372)
Partially implements https://github.com/paritytech/polkadot-sdk/issues/5048 - adds a core selection runtime API to cumulus and a generic way of configuring it for a parachain - modifies the slot based collator to utilise the claim queue and the generic core selection What's left to be implemented (in a follow-up PR): - add the UMP signal for core selection into the parachain-system pallet View the RFC for more context: https://github.com/polkadot-fellows/RFCs/pull/103 --------- Co-authored-by: command-bot <>