Rococo/Westend Coretime Runtime

New runtimes for the Coretime Chain (a.k.a. "Broker Chain") described in
RFC-1.

Replaces https://github.com/paritytech/cumulus/pull/2889


- [x] Add Agile Coretime pallet
https://github.com/paritytech/substrate/pull/14568
- [x] Generate chain specs for local and testnets
- [x] Deploy parachain on Rococo - Done:
[rococo-coretime-rpc.polkadot.io](https://polkadot.js.org/apps/?rpc=wss%3A%2F%2Frococo-coretime-rpc.polkadot.io#/explorer)

DevOps issue for Aura keygen:
https://github.com/paritytech/devops/issues/2725

Edit (Dónal): This PR is mainly for Rococo, the Westend runtime is a
shell with no `Broker` pallet. The Rococo runtime has the broker calls
filtered for initial deployment.

---------

Co-authored-by: Dónal Murray <donal.murray@parity.io>
Co-authored-by: 0xmovses <r.v.melkonian@gmail.com>
Co-authored-by: Liam Aharon <liam.aharon@hotmail.com>
Co-authored-by: Bastian Köcher <git@kchr.de>
Co-authored-by: Marcin S. <marcin@realemail.net>
Co-authored-by: Bastian Köcher <info@kchr.de>
Co-authored-by: command-bot <>
Co-authored-by: Branislav Kontur <bkontur@gmail.com>

substrate/frame/broker/src/tick_impls.rs

@@ -112,10 +112,16 @@ impl<T: Config> Pallet<T> {
 		}
 		// Payout system InstaPool Cores.
 		let total_contrib = r.system_contributions.saturating_add(r.private_contributions);
-		let system_payout =
-			revenue.saturating_mul(r.system_contributions.into()) / total_contrib.into();
-		let _ = Self::charge(&Self::account_id(), system_payout);
-		revenue.saturating_reduce(system_payout);
+		let system_payout = if !total_contrib.is_zero() {
+			let system_payout =
+				revenue.saturating_mul(r.system_contributions.into()) / total_contrib.into();
+			let _ = Self::charge(&Self::account_id(), system_payout);
+			revenue.saturating_reduce(system_payout);
+
+			system_payout
+		} else {
+			Zero::zero()
+		};
 
 		if !revenue.is_zero() && r.private_contributions > 0 {
 			r.maybe_payout = Some(revenue);