Westend/Rococo Asset Hub: pay xcm fees with sufficient assets (#2978)
Set up the `TakeFirstAssetTrader` trader for Westend and Rococo Asset
Hubs to cover XCM fees with sufficient assets.
This PR reintroduces previously
[removed](https://github.com/paritytech/polkadot-sdk/pull/1845) trader
setups, as it was decided to keep both traders, `TakeFirstAssetTrader`
and `SwapFirstAssetTrader`, during the transition period.
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Co-authored-by: Svyatoslav Nikolsky <[email protected]>