Unified send doesn't support lnurl

[benthecarman]

We use ldk's LDKOnionMessageDNSSECHrnResolver to resolve HRNs which doesn't support lnurl.

Some options to fix this:

• Replace LDKOnionMessageDNSSECHrnResolver with HttpResolver: simplest but loses privacy benefits
• Update LDKOnionMessageDNSSECHrnResolver to optionally support lnurl through providing a http resolver
• Update bitcoin-payment-instructions to support providing multiple resolvers.

[tnull]

Note there will be quite a bit of resolution-related changes coming as part of #630.

However, it seems to me that either one of these might be the way to go

• Update LDKOnionMessageDNSSECHrnResolver to optionally support lnurl through providing a http resolver
• Update bitcoin-payment-instructions to support providing multiple resolvers.

We definitely shouldn't revert he BIP353 changes in favor of LNURL.

Not sure if @TheBlueMatt has an opionion on the preferred approach?