Human Readable Names Support

[TheBlueMatt]

bitcoin/bips#1551 describes a mechanism for mapping human-readable names (in the Buser@domain form) to BIP 21 URIs (targeting mostly silent payment addresses and BOLT12 offers). It would be nice if BDK came with support built-in for doing the lookups (or at least verifying DNSSEC proofs using https://git.bitcoin.ninja/index.cgi?p=dnssec-prover) and mapping them to a BIP 21 URI (and then resolving that to payment instructions).

We should probably have a discussion about where this kind of general payment instruction lookup logic should live - maybe LDK should refactor its BOLT12 offer and BOLT11 invoice parsing code into crates that don't depend on lightning so that we can have some generic "bitcoin payment instruction resolver" crate that BDK and LDK can use to resolve human readable names/BIP 21 URIs/bitcoin addresses to a list of payment instructions.