pallet-session: Migrate the historical part to the new pallet macro (#9878)

* Migrate session-historical to the new pallet macro

Signed-off-by: koushiro <koushiro.cqx@gmail.com>

* pallet-session: Migrate the historical part to the new pallet macro

Signed-off-by: koushiro <koushiro.cqx@gmail.com>

* Fix staking test runtime

Signed-off-by: koushiro <koushiro.cqx@gmail.com>

* Update frame/session/src/historical/mod.rs

* Update frame/session/src/historical/mod.rs

* update migration doc

Signed-off-by: koushiro <koushiro.cqx@gmail.com>

* use hardcoded prefix for migration v1

Signed-off-by: koushiro <koushiro.cqx@gmail.com>

* cargo +nightly-2021-11-08 fmt

Signed-off-by: koushiro <koushiro.cqx@gmail.com>

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

substrate/frame/session/src/migrations/mod.rs

@@ -0,0 +1,24 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2019-2021 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+/// Version 1.
+///
+/// In version 0 session historical pallet uses `Session` for storage module prefix.
+/// In version 1 it uses its name as configured in `construct_runtime`.
+/// This migration moves session historical pallet storages from old prefix to new prefix.
+#[cfg(feature = "historical")]
+pub mod v1;