Staking AH Client: bound `OutgoingValidatorSet`

[kianenigma]

Create a proper bound for this type as having unbounded storage items in a parachain is frowned upon.

polkadot-sdk/substrate/frame/staking-async/rc-client/src/lib.rs

Lines 621 to 630 in 18f6251

	/// A validator set that is outgoing, and should be sent.
	///
	/// This will be attempted to be sent, possibly on every `on_initialize` call, until it is sent,
	/// or the second value reaches zero, at which point we drop it.
	#[pallet::storage]
	// TODO: for now we know this ValidatorSetReport is at most validator-count * 32, and we don't
	// need its MEL critically.
	#[pallet::unbounded]
	pub type OutgoingValidatorSet<T: Config> =
	StorageValue<_, (ValidatorSetReport<T::AccountId>, u32), OptionQuery>;

[kdonthi]

I can take a shot at this :)

[kdonthi]

#10197

[kdonthi]

@kianenigma could I please get a review :)