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/runtimes/testing/penpal/Cargo.toml

@@ -77,7 +77,6 @@ cumulus-primitives-utility = { path = "../../../../primitives/utility", default-
 pallet-collator-selection = { path = "../../../../pallets/collator-selection", default-features = false }
 parachain-info = { package = "staging-parachain-info", path = "../../../pallets/parachain-info", default-features = false }
 parachains-common = { path = "../../../common", default-features = false }
-testnet-parachains-constants = { path = "../../constants", default-features = false, features = ["rococo"] }
 assets-common = { path = "../../assets/common", default-features = false }
 
 [features]
@@ -133,7 +132,6 @@ std = [
 	"sp-transaction-pool/std",
 	"sp-version/std",
 	"substrate-wasm-builder",
-	"testnet-parachains-constants/std",
 	"xcm-builder/std",
 	"xcm-executor/std",
 	"xcm/std",