Implement Magic Routing Hint Shortcut (BTC->LN->L-BTC to BTC->L-BTC)

[kilrau]

Problem:

Currently, when users try to "top up" their "Lightning balance" in Aqua & other similar Boltz-powered liquid wallets with Bitcoin using a BTC -> LN swap via our Web App, this fails with a "preimage hash already exists" error as they are chaining two swaps, which we are preventing.

Solution:

Our WebApp should interpret Magic Routing Hints in the Boltz Lightning invoice, the same way other clients do and automatically switch to a direct BTC -> L-BTC swap if a magic routing hint is included in a BTC -> LN swap. At the moment this applies for this one specific case only, as we are only embedding Magic Routing Hints for Liquid but we might have more in future.