Treasury spends various asset kinds (#1333)

### Summary 

This PR introduces new dispatchables to the treasury pallet, allowing
spends of various asset types. The enhanced features of the treasury
pallet, in conjunction with the asset-rate pallet, are set up and
enabled for Westend and Rococo.

### Westend and Rococo runtimes.

Polkadot/Kusams/Rococo Treasury can accept proposals for `spends` of
various asset kinds by specifying the asset's location and ID.

#### Treasury Instance New Dispatchables:
- `spend(AssetKind, AssetBalance, Beneficiary, Option<ValidFrom>)` -
propose and approve a spend;
- `payout(SpendIndex)` - payout an approved spend or retry a failed
payout
- `check_payment(SpendIndex)` - check the status of a payout;
- `void_spend(SpendIndex)` - void previously approved spend;
> existing spend dispatchable renamed to spend_local

in this context, the `AssetKind` parameter contains the asset's location
and it's corresponding `asset_id`, for example:
`USDT` on `AssetHub`,
``` rust
location = MultiLocation(0, X1(Parachain(1000)))
asset_id = MultiLocation(0, X2(PalletInstance(50), GeneralIndex(1984)))
```

the `Beneficiary` parameter is a `MultiLocation` in the context of the
asset's location, for example
``` rust
// the Fellowship salary pallet's location / account
FellowshipSalaryPallet = MultiLocation(1, X2(Parachain(1001), PalletInstance(64)))
// or custom `AccountId`
Alice = MultiLocation(0, AccountId32(network: None, id: [1,...]))
```

the `AssetBalance` represents the amount of the `AssetKind` to be
transferred to the `Beneficiary`. For permission checks, the asset
amount is converted to the native amount and compared against the
maximum spendable amount determined by the commanding spend origin.

the `spend` dispatchable allows for batching spends with different
`ValidFrom` arguments, enabling milestone-based spending. If the
expectations tied to an approved spend are not met, it is possible to
void the spend later using the `void_spend` dispatchable.

Asset Rate Pallet provides the conversion rate from the `AssetKind` to
the native balance.

#### Asset Rate Instance Dispatchables:
- `create(AssetKind, Rate)` - initialize a conversion rate to the native
balance for the given asset
- `update(AssetKind, Rate)` - update the conversion rate to the native
balance for the given asset
- `remove(AssetKind)` - remove an existing conversion rate to the native
balance for the given asset

the pallet's dispatchables can be executed by the Root or Treasurer
origins.

### Treasury Pallet

Treasury Pallet can accept proposals for `spends` of various asset kinds
and pay them out through the implementation of the `Pay` trait.

New Dispatchables:
- `spend(Config::AssetKind, AssetBalance, Config::Beneficiary,
Option<ValidFrom>)` - propose and approve a spend;
- `payout(SpendIndex)` - payout an approved spend or retry a failed
payout;
- `check_payment(SpendIndex)` - check the status of a payout;
- `void_spend(SpendIndex)` - void previously approved spend;
> existing spend dispatchable renamed to spend_local

The parameters' types of the `spend` dispatchable exposed via the
pallet's `Config` and allows to propose and accept a spend of a certain
amount.

An approved spend can be claimed via the `payout` within the
`Config::SpendPeriod`. Clients provide an implementation of the `Pay`
trait which can pay an asset of the `AssetKind` to the `Beneficiary` in
`AssetBalance` units.

The implementation of the Pay trait might not have an immediate final
payment status, for example if implemented over `XCM` and the actual
transfer happens on a remote chain.

The `check_status` dispatchable can be executed to update the spend's
payment state and retry the `payout` if the payment has failed.

---------

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>
Co-authored-by: command-bot <>

cumulus/parachains/runtimes/assets/asset-hub-westend/src/xcm_config.rs

@@ -38,11 +38,12 @@ use xcm::latest::prelude::*;
 use xcm_builder::{
 	AccountId32Aliases, AllowExplicitUnpaidExecutionFrom, AllowKnownQueryResponses,
 	AllowSubscriptionsFrom, AllowTopLevelPaidExecutionFrom, CurrencyAdapter,
-	DenyReserveTransferToRelayChain, DenyThenTry, EnsureXcmOrigin, FungiblesAdapter, IsConcrete,
-	LocalMint, NativeAsset, NoChecking, ParentAsSuperuser, ParentIsPreset, RelayChainAsNative,
-	SiblingParachainAsNative, SiblingParachainConvertsVia, SignedAccountId32AsNative,
-	SignedToAccountId32, SovereignSignedViaLocation, TakeWeightCredit, TrailingSetTopicAsId,
-	UsingComponents, WeightInfoBounds, WithComputedOrigin, WithUniqueTopic,
+	DenyReserveTransferToRelayChain, DenyThenTry, DescribeFamily, DescribePalletTerminal,
+	EnsureXcmOrigin, FungiblesAdapter, HashedDescription, IsConcrete, LocalMint, NativeAsset,
+	NoChecking, ParentAsSuperuser, ParentIsPreset, RelayChainAsNative, SiblingParachainAsNative,
+	SiblingParachainConvertsVia, SignedAccountId32AsNative, SignedToAccountId32,
+	SovereignSignedViaLocation, TakeWeightCredit, TrailingSetTopicAsId, UsingComponents,
+	WeightInfoBounds, WithComputedOrigin, WithUniqueTopic,
 };
 use xcm_executor::{traits::WithOriginFilter, XcmExecutor};
 
@@ -75,6 +76,9 @@ pub type LocationToAccountId = (
 	SiblingParachainConvertsVia<Sibling, AccountId>,
 	// Straight up local `AccountId32` origins just alias directly to `AccountId`.
 	AccountId32Aliases<RelayNetwork, AccountId>,
+	// Foreign chain account alias into local accounts according to a hash of their standard
+	// description.
+	HashedDescription<AccountId, DescribeFamily<DescribePalletTerminal>>,
 );
 
 /// Means for transacting the native currency on this chain.
@@ -222,6 +226,9 @@ match_types! {
 		MultiLocation { parents: 1, interior: Here } |
 		MultiLocation { parents: 1, interior: X1(Plurality { .. }) }
 	};
+	pub type TreasuryPallet: impl Contains<MultiLocation> = {
+		MultiLocation { parents: 1, interior: X1(PalletInstance(37)) }
+	};
 }
 
 /// A call filter for the XCM Transact instruction. This is a temporary measure until we properly
@@ -449,8 +456,9 @@ pub type Barrier = TrailingSetTopicAsId<
 					// If the message is one that immediately attemps to pay for execution, then
 					// allow it.
 					AllowTopLevelPaidExecutionFrom<Everything>,
-					// Parent and its pluralities (i.e. governance bodies) get free execution.
-					AllowExplicitUnpaidExecutionFrom<ParentOrParentsPlurality>,
+					// Parent, its pluralities (i.e. governance bodies) and treasury pallet get
+					// free execution.
+					AllowExplicitUnpaidExecutionFrom<(ParentOrParentsPlurality, TreasuryPallet)>,
 					// Subscriptions for version tracking are OK.
 					AllowSubscriptionsFrom<Everything>,
 				),