Add integration with pallet_offences + pallet_session::historical

[NachoPal]

This PR intends to add capability for automatic removal of disabled validators. It would be an optional feature to be integrated along with pallet_offences and pallet_session::historical.

validator_set implements OnOffenceHandler trait which is expected by type OnOffenceHandler in pallet_offences::Config.

Trait implementation expects Offender to be pallet_session::historical::IdentificationTuple<T>.

Added two new Config types:

• OnDisabled: action to be executed when a validator is disabled
• MinAuthoritiesOnDisabled: boolean that indicates whether MinAuthorities should be checked before removing a disabled validator from the next active set.

Two new Config types could be added for more granularity in the im_online integration:

• OnOffline: action to be executed when a validator is offline.
• MinAuthoritiesOnOffline: boolean that indicates whether MinAuthorities should be checked before removing an offline validator from the next active set.

Example of runtime configuration:

parameter_types! {
	pub const MinAuthorities: u32 = 2;
	pub const MinAuthoritiesOnDisabled: bool = true;
}

impl validator_set::Config for Runtime {
	type RuntimeEvent = RuntimeEvent;
	type AddRemoveOrigin = EnsureRoot<AccountId>;
	type MinAuthorities = MinAuthorities;
	type OnDisabled = ();
	type MinAuthoritiesOnDisabled = MinAuthoritiesOnDisabled;
	type WeightInfo = validator_set::weights::SubstrateWeight<Runtime>;
}

impl pallet_session::historical::Config for Runtime {
	type FullIdentification = Self::ValidatorId;
	type FullIdentificationOf = Self::ValidatorIdOf;
}

impl pallet_offences::Config for Runtime {
	type RuntimeEvent = RuntimeEvent;
	type IdentificationTuple = pallet_session::historical::IdentificationTuple<Self>;
	type OnOffenceHandler = ValidatorSet;
}