add pallet nomination-pools versioned migration to kitchensink (#2167)

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

https://github.com/paritytech/polkadot-sdk/blob/f6ee4781f633f0f89598f7b230595afe401da8dc/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`.

polkadot/runtime/westend/src/lib.rs

@@ -1533,9 +1533,9 @@ pub mod migrations {
 		parachains_configuration::migration::v8::MigrateToV8<Runtime>,
 		parachains_configuration::migration::v9::MigrateToV9<Runtime>,
 		paras_registrar::migration::MigrateToV1<Runtime, ()>,
-		pallet_nomination_pools::migration::versioned_migrations::V5toV6<Runtime>,
+		pallet_nomination_pools::migration::versioned::V5toV6<Runtime>,
 		pallet_referenda::migration::v1::MigrateV0ToV1<Runtime, ()>,
-		pallet_nomination_pools::migration::versioned_migrations::V6ToV7<Runtime>,
+		pallet_nomination_pools::migration::versioned::V6ToV7<Runtime>,
 		pallet_grandpa::migrations::MigrateV4ToV5<Runtime>,
 		parachains_configuration::migration::v10::MigrateToV10<Runtime>,
 	);

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