Reverse Swaps: Store Direct Addresses into routing hints of invoice

[kilrau]

Successor of https://github.com/BoltzExchange/boltz-backend/issues/455 (which is an undocumented temporary feature): we want to enable a more robust way of setting a "direct address" by storing it in the routing hints table of an invoice instead of poluting the invoice memo.

What are Direct Addresses? A direct address of e.g. a Liquid Reverse Swap is a new Liquid Address of the underlying liquid wallet that the sender can optionally use instead of paying the swap invoice if his wallet is on Liquid too. For the famous use case of Aqua to Aqua payments, this then results in a much cheaper plain Liquid transfer instead of a Liquid -> Lightning -> Liquid swap. Should work for all supported chains.