Bridging: Add pallet-assets (#2354)

## Description

In order to **teleport Frequency tokens to AssetHub**, we need a way to
pay the execution fee on **AssetHub otherwise it will reject the
request** and treat the tokens as **trapped assets**.

Since **AssetHub does not accept Frequency** as payment for execution
fees, we must also include DOT in the message to cover those fees.

To support this, Frequency must be able to handle DOT as an asset — both
to receive DOT from AssetHub and to **send DOT back out**.

## Acceptance Criteria
- [ ] Add the ability to send and receive DOT on Frequency
- [ ] Store DOT as a Multilocation on Frequency
- [ ] Decide who should be allowed to create assets on Frequency
- [x] Generate Weights
- [x] Feature Flag `frequency-bridging`

Implementation suggestions
- User Pallet Assets
- Config

```
pallet-assets = { workspace = true, default-features = false }
```

```
parameter_types! {
	pub const AssetDeposit: Balance = 0;
	pub const AssetAccountDeposit: Balance = 0;
	pub const ApprovalDeposit: Balance = 0;
	pub const AssetsStringLimit: u32 = 50;
	pub const MetadataDepositBase: Balance = 0;
	pub const MetadataDepositPerByte: Balance = 0;
}

parameter_types! {
	// we just reuse the same deposits
	pub const ForeignAssetsAssetDeposit: Balance = AssetDeposit::get();
	pub const ForeignAssetsAssetAccountDeposit: Balance = AssetAccountDeposit::get();
	pub const ForeignAssetsApprovalDeposit: Balance = ApprovalDeposit::get();
	pub const ForeignAssetsAssetsStringLimit: u32 = AssetsStringLimit::get();
	pub const ForeignAssetsMetadataDepositBase: Balance = MetadataDepositBase::get();
	pub const ForeignAssetsMetadataDepositPerByte: Balance = MetadataDepositPerByte::get();
}
```

```
use xcm_config::{RelayLocation, XcmOriginToTransactDispatchOrigin, ForeignAssetsAssetId};
impl pallet_assets::Config  for Runtime {
	type RuntimeEvent = RuntimeEvent;
	type Balance = Balance;
////
	type AssetId = ForeignAssetsAssetId;
	type AssetIdParameter = ForeignAssetsAssetId;
	type Currency = Balances;
	// This is to allow any other remote location to create foreign assets. Used in tests, not
	// recommended on real chains.
	type **CreateOrigin** =
		**ForeignCreators**<Everything, LocationToAccountId, AccountId, xcm::latest::Location>;
	type ForceOrigin = EnsureRoot<AccountId>;
	type AssetDeposit = ForeignAssetsAssetDeposit;
	type MetadataDepositBase = ForeignAssetsMetadataDepositBase;
	type MetadataDepositPerByte = ForeignAssetsMetadataDepositPerByte;
	type ApprovalDeposit = ForeignAssetsApprovalDeposit;
	type StringLimit = ForeignAssetsAssetsStringLimit;
	type Freezer = ();
	type Extra = ();
	type WeightInfo = pallet_assets::weights::SubstrateWeight<Runtime>;
	type CallbackHandle = ();
	type AssetAccountDeposit = ForeignAssetsAssetAccountDeposit;
	type RemoveItemsLimit = frame_support::traits::ConstU32<1000>;
	#[cfg(feature = "runtime-benchmarks")]
	type BenchmarkHelper = xcm_config::XcmBenchmarkHelper;
	type Holder = ();
}
```

# Checklist
- [ ] Updated Pallet Readme?
- [ ] Updated js/api-augment for Custom RPC APIs?
- [ ] Design doc(s) updated?
- [ ] Unit Tests added?
- [ ] e2e Tests added?
- [ ] Benchmarks added?
- [x] Spec version incremented?

Author: mattheworris

Cargo.lock

@@ -78,6 +78,9 @@ pallet-transaction-payment-rpc-runtime-api = { git = "https://github.com/parityt
 pallet-utility = { git = "https://github.com/paritytech/polkadot-sdk", branch = "stable2503", default-features = false }
 pallet-proxy = { git = "https://github.com/paritytech/polkadot-sdk", branch = "stable2503", default-features = false }
 
+# Bridging Pallets
+pallet-assets = { git = "https://github.com/paritytech/polkadot-sdk", branch = "stable2503", default-features = false }
+
 # polkadot
 polkadot-cli = { git = "https://github.com/paritytech/polkadot-sdk", branch = "stable2503" }
 polkadot-parachain-primitives = { git = "https://github.com/paritytech/polkadot-sdk", branch = "stable2503", default-features = false }

Cargo.toml

@@ -8,10 +8,16 @@ all: build
 clean:
 	cargo clean
 
-.PHONY: start start-frequency start-frequency-docker start-manual start-interval start-interval-short start-with-offchain start-frequency-with-offchain start-manual-with-offchain start-interval-with-offchain
+.PHONY: start start-bridging start-bridging-westend start-frequency start-frequency-docker start-manual start-interval start-interval-short start-with-offchain start-frequency-with-offchain start-manual-with-offchain start-interval-with-offchain
 start:
 	./scripts/init.sh start-frequency-instant
 
+start-bridging:
+	./scripts/init.sh start-frequency-instant-bridging
+
+start-bridging-westend:
+	./scripts/init.sh start-frequency-westend-bridging
+
 start-paseo-relay:
 	./scripts/init.sh start-paseo-relay-chain
 
@@ -90,7 +96,7 @@ register:
 onboard:
 	./scripts/init.sh onboard-frequency-paseo-local
 
-.PHONY: onboard-res-local
+.PHONY: onboard-debug
 onboard-debug:
 	./scripts/init.sh onboard-res-local
 
@@ -244,7 +250,11 @@ docs:
 docker-prune:
 	./scripts/prune_all.sh
 
-.PHONY: check check-no-relay check-local check-testnet check-mainnet
+.PHONY: check check-no-relay check-local check-testnet check-mainnet check-bridging
+# Add a target to run all checks to check that all existing features work with the addition of 'frequency-bridging'
+# which is an add-on feature and not mutually exclusive with the other features.
+check-all: check check-no-relay check-local check-testnet check-mainnet check-bridging
+
 check:
 	SKIP_WASM_BUILD= cargo check --features runtime-benchmarks,frequency-lint-check
 
@@ -260,11 +270,20 @@ check-testnet:
 check-mainnet:
 	SKIP_WASM_BUILD= cargo check --features frequency
 
+check-bridging:
+	SKIP_WASM_BUILD= cargo check --features frequency,frequency-bridging
+	SKIP_WASM_BUILD= cargo check --features frequency-testnet,frequency-bridging
+	SKIP_WASM_BUILD= cargo check --features frequency-local,frequency-bridging
+
+
 .PHONY: js
 js:
 	./scripts/generate_js_definitions.sh
 
-.PHONY: build build-benchmarks build-no-relay build-local build-testnet build-mainnet build-testnet-release build-mainnet-release
+.PHONY: build build-benchmarks build-no-relay build-local build-testnet build-mainnet build-testnet-release build-mainnet-release build-bridging-mainnet build-bridging-westend build-all
+
+build-all: build build-benchmarks build-no-relay build-local build-testnet build-mainnet build-testnet-release build-mainnet-release build-bridging-mainnet build-bridging-westend
+
 build:
 	cargo build --features frequency-no-relay
 
@@ -289,6 +308,12 @@ build-testnet-release:
 build-mainnet-release:
 	cargo build --locked --features  frequency --release
 
+build-bridging-mainnet:
+	cargo build --features frequency,frequency-bridging
+
+build-bridging-westend:
+	cargo build --features frequency-local,frequency-bridging
+
 .PHONY: test e2e-tests e2e-tests-serial e2e-tests-only e2e-tests-load e2e-tests-load-only e2e-tests-testnet-paseo e2e-tests-paseo-local
 test:
 	cargo test --workspace --features runtime-benchmarks,frequency-lint-check

Makefile

@@ -50,6 +50,7 @@ frequency-testnet = []
 frequency-local = []
 frequency-no-relay = []
 runtime-benchmarks = ["pallet-collective/runtime-benchmarks"]
+frequency-bridging = []
 std = [
   "frame-support/std",
   "frame-system/std",