Tracking: interoperability bugs when making offer payments

[orbitalturtle]

I've been testing offer payments with our new lndk-cli pay-offer command: #91

Just using this issue to keep tabs on some problems we've encountered when making offer payments to various lightning implementations.

Payment to CLN offer:

• Offers: not getting invoice back after sending invoice request for CLN offer ElementsProject/lightning#7110
• Blinded route should hold alias instead of actual scid? ElementsProject/lightning#6588
  Not 100% if this was a config option issue on my part or... something else.

Payment to LDK-sample offer:

• Prefer non-onion nodes in blinded paths lightningdevkit/rust-lightning#2893
• Fix ser for PaymentRelay and PaymentConstraints lightningdevkit/rust-lightning#2936
  • This bug is now fixed! Once rust-lightning v122 is out and ldk-sample supports it, we can again try to make a payment to a ldk-sample offer with Eclair or CLN as the introduction node.