Make penpal-runtime's TrustedReserves more connfigurable (#3564)

The current `penpal` runtime utilizes the `EthereumLocation` parameter,
which is employed for XCM emulated integration tests concerning the
Rococo <> ETH bridge. It includes a hard-coded chainId for the Ethereum
testnet utilized in Rococo. The `EthereumLocation` serves the purpose of
aligning with the `TrustedReserves`. However, due to this hard-coded
configuration, reusing `penpal` for testing various environments such as
Kusama/Polkadot versus Ethereum bridge becomes unfeasible.

This PR introduces the capability to easily customize the asset location
for `TrustedReserves` without needing to know anything about Ethereum.


## TODO
- [x] fix integration tests with
`System::set_storage(CustomizableAssetFromSystemAssetHub::key(),
<whatever-location-is-needed>)` @claravanstaden
- [ ] ~~maybe add some helper function/macro to support `set_storage`
for other runtimes (that we could reuse)~~
- [ ] Release patch for: `penpal-runtime` + emulated crate with
`set_storage` support (if needed)
  - [ ] backport to 1.7.0
  - [ ] backport to 1.8.0

---------

Co-authored-by: Clara van Staden <claravanstaden64@gmail.com>

cumulus/parachains/integration-tests/emulated/tests/bridges/bridge-hub-rococo/src/tests/snowbridge.rs

@@ -18,6 +18,7 @@ use codec::{Decode, Encode};
 use emulated_integration_tests_common::xcm_emulator::ConvertLocation;
 use frame_support::pallet_prelude::TypeInfo;
 use hex_literal::hex;
+use rococo_system_emulated_network::penpal_emulated_chain::CustomizableAssetFromSystemAssetHub;
 use rococo_westend_system_emulated_network::BridgeHubRococoParaSender as BridgeHubRococoSender;
 use snowbridge_core::outbound::OperatingMode;
 use snowbridge_pallet_inbound_queue_fixtures::{
@@ -253,6 +254,16 @@ fn send_token_from_ethereum_to_penpal() {
 		(PenpalASender::get(), INITIAL_FUND),
 	]);
 
+	PenpalA::execute_with(|| {
+		assert_ok!(<PenpalA as Chain>::System::set_storage(
+			<PenpalA as Chain>::RuntimeOrigin::root(),
+			vec![(
+				CustomizableAssetFromSystemAssetHub::key().to_vec(),
+				Location::new(2, [GlobalConsensus(Ethereum { chain_id: CHAIN_ID })]).encode(),
+			)],
+		));
+	});
+
 	// The Weth asset location, identified by the contract address on Ethereum
 	let weth_asset_location: Location =
 		(Parent, Parent, EthereumNetwork::get(), AccountKey20 { network: None, key: WETH }).into();