Marketplace fee

[olanod]

We need to define a standard format for the payment remark to be used by marketplaces to detect when a payment should leave a fee to the marketplace.

One option is to use a human readable format like JSON but comes at the cost of more expensive parsing and extra size(specially if the payload needs to include signatures for example), the alternative is to use SCALE that will be more efficient and take less space but requires extra work in the client. As we usually expect payments to be done from a custom client that is familiar with SCALE I'd opt for this option. On top of this to get better support in polkadot.js for the remark, it might be better for remarks to be typed(implementing Encode) instead of opaque bytes.

#[derive(Encode, Decode, TypeInfo)]
enum VirtoPaymentRemark {
    V0(CommunityId), // community id is checked to be a valid marketplace with a configured fee
}