add pallet nomination-pools versioned migration to kitchensink (parit…

…ytech#2167)

The versioned migrations are already there in pallet nomination-pools:

https://github.com/paritytech/polkadot-sdk/blob/1766468c930299358fc13940e50d973fe734ba5c/substrate/frame/nomination-pools/src/migration.rs#L27-L48

Just updating the kitchensink runtime to point to them.

This is also nice because it points the dev to an example of how to use
`VersionedMigration`.

substrate/bin/node/runtime/src/lib.rs

@@ -2194,9 +2194,10 @@ pub type Executive = frame_executive::Executive<
 >;
 
 // All migrations executed on runtime upgrade as a nested tuple of types implementing
-// `OnRuntimeUpgrade`.
+// `OnRuntimeUpgrade`. Note: These are examples and do not need to be run directly
+// after the genesis block.
 type Migrations = (
-	pallet_nomination_pools::migration::v2::MigrateToV2<Runtime>,
+	pallet_nomination_pools::migration::versioned::V6ToV7<Runtime>,
 	pallet_alliance::migration::Migration<Runtime>,
 	pallet_contracts::Migration<Runtime>,
 );

substrate/frame/nomination-pools/src/migration.rs

@@ -24,7 +24,7 @@ use sp_std::{collections::btree_map::BTreeMap, vec::Vec};
 use sp_runtime::TryRuntimeError;
 
 /// Exports for versioned migration `type`s for this pallet.
-pub mod versioned_migrations {
+pub mod versioned {
 	use super::*;
 
 	/// Migration V6 to V7 wrapped in a [`frame_support::migrations::VersionedMigration`], ensuring