XCM oracle for asset prices

[olanod]

To allow communities to pay fees in their own asset we need a way to price them, sufficient assets are trusted to have value and a minimum balance that can be used as reference to charge fees, for new assets however we can not easily trust the minimum balance and using a price from a decentralized exchange is a better reference.

We want to help communities set up a trading pool in Kusama AssetHub that Kreivo can query on regular basis to refresh its knowledge of the price of a given asset, scheduled XCM queries can help us get the price information in a trustless manner.