Move PalletVersion away from the crate version (#9165)

* Move `PalletVersion` away from the crate version

Before this pr, `PalletVersion` was referring to the crate version that
hosted the pallet. This pr introduces a custom `package.metadata.frame`
section in the `Cargo.toml` that can contain a `pallet-version` key
value pair. While the value is expected to be a valid u16. If this
key/value pair isn't given, the version is set to 1.

It also changes the `PalletVersion` declaration. We now only have one
`u16` that represents the version. Not a major/minor/patch version. As
the old `PalletVersion` was starting with the `u16` major, decoding the
old values will work.

* Overhaul the entire implementation

- Drop PalletVersion
- Introduce StorageVersion
- StorageVersion needs to be set in the crate and set for the macros
- Added migration

* Fix migrations

* Review feedback

* Remove unneeded dep

* remove pub consts

* Brings back logging and implements `GetStorageVersion`

* Return weight from migration

* Fmt and remove unused import

* Update frame/support/src/dispatch.rs

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

* Update frame/support/src/traits/metadata.rs

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

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

substrate/frame/elections-phragmen/src/lib.rs

@@ -104,7 +104,7 @@ use frame_support::{
 	traits::{
 		ChangeMembers, Contains, ContainsLengthBound, Currency, CurrencyToVote, Get,
 		InitializeMembers, LockIdentifier, LockableCurrency, OnUnbalanced, ReservableCurrency,
-		SortedMembers, WithdrawReasons,
+		SortedMembers, StorageVersion, WithdrawReasons,
 	},
 	weights::Weight,
 };
@@ -122,6 +122,9 @@ pub use weights::WeightInfo;
 /// All migrations.
 pub mod migrations;
 
+/// The current storage version.
+const STORAGE_VERSION: StorageVersion = StorageVersion::new(4);
+
 /// The maximum votes allowed per voter.
 pub const MAXIMUM_VOTE: usize = 16;
 
@@ -239,6 +242,7 @@ pub mod pallet {
 
 	#[pallet::pallet]
 	#[pallet::generate_store(pub(super) trait Store)]
+	#[pallet::storage_version(STORAGE_VERSION)]
 	pub struct Pallet<T>(PhantomData<T>);
 
 	#[pallet::hooks]